Fingerprinting Air

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"Even where the criminal makes no attempt to efface the prints of his fingers, but leaves them all over the scene of the crime, the chances are about one in ten of finding a print that is sufficiently clear to be of any value." —Dashiell Hammett, The Smart Set

In fictionland, you can get a fingerprint off of anything, including human skin. Most of the time, you'll get a complete print suitable for analysis. If you get a partial, odds are that it's still good enough for analysis. You can also get a sample good enough for identification by fingerprinting a heavily decomposed corpse. Everyone in the world has their fingerprints on file, so an AFIS search is always going to come back with something (but then, it is a Magical Database). No one even takes the precaution of wearing gloves, which is a common practice among criminals, although it is sometimes possible to leave a fingerprint impression through thin gloves. The AFIS match is always conclusive.

In the real world, an examiner looks at a list of possible matches generated from the database—computer pattern matching is much more basic and can contain lots of false positives. Also, mistakes are possible, albeit rare. In 2005, three experienced FBI examiners mis-identified Brandon Mayfield as a suspect in the Madrid Bombings. A fourth expert hired by the court went along with the results. The mistake later came to light when the Spanish authorities disagreed with the result.

Fingerprinting in the real world is not quite so easy, but there are one or two places where the shows catch a break. CSI benefits from being set in Las Vegas, where the largest employers (the casinos) require employees to register with the gaming commission. The use of superglue fumes to process latent fingerprints is, surprisingly, quite real. While not quite so miraculous as it appears on TV, it certainly must have seemed that way when it was first discovered.

Fingerprinting also tends to be so common in fiction that lack of fingerprints is taken as evidence of someone interfering with evidence. No one ever lacks fingerprints unless they're a criminal, everyone has a full set of prints, no one gets one burnt off by accident.

DNA works the same way as fingerprints. Anything the perp has licked, touched, or sweat on can incriminate them. In real life, suitable DNA for comparison is harder to get, comparisons takes days, not minutes, and the percentage of people listed in CODIS is very small indeed. Until the past few years, DNA comparisons were impossible without a very large sample, and the technology to compare small samples is still of limited availability.

On the other hand, if it's not the kind of show where science saves the day, the best crime scene team in the world isn't going to find a single print. Columbo, in 35 years, only had three cases broken by fingerprints. (In one, it was prints on the insides of gloves. One where the gun used was wiped of prints but not the bullets. In another, the bad guy was actually caught because Columbo's prints were on the evidence. Yeah, it's a long story.)

The trope name comes from an exchange on CSI, possibly the worst offender. A detective asks Warrick if he can pull a print from some object, and he exaggerates, "I can pull a fingerprint off the air."

Examples of Fingerprinting Air include:

Comic Books

• DNA version. Subverted in Spider-Man in which Spidey is confronted with a woman who claims to be the daughter of his former girlfriend, Gwen Stacy. He happens to have a letter from Gwen but notes that he can't use it to obtain a DNA sample because it's quite simply too old by this point, forcing him to retrieve a sample from her grave.
• Dick Tracy was once left a message by a perp in alphabet blocks on a drugstore counter, left there for customers to play with. It was taken in for fingerprinting. When he checked up with Forensics later, they responded that the blocks must've been handled by just about everyone who passed through the store.

Film

• In The Dark Knight, Batman is able to get fingerprints from a bullet by removing the piece of wall in which it had hit and using a computer program to reassemble the bullet, and get a fingerprint from THAT. Never mind that the fragments would probably be warped, or that the impact and friction would have utterly destroyed any semblance of a fingerprint, or the fact that the print would not be on the bullet but the shell casing, Batman is just that goddamn awesome.
• In Se7en, the trope is initially averted when the killer deliberately coats a wall with prints, yet it still takes the finger print analysis team many man hours to identify the source. Played straight, with the killer going to excessive lengths to avoid leaving any of his own finger prints anywhere (where latex gloves could have easily sufficed).
• In Fast Five Tej is able to lift a full hand print off of a bikini, and it good enough to get through a high end scanner.

Literature

• Aversion in the novel Gorky Park, Renko and an American detective are dusting a woodshop for fingerprints, and someone points out some rags that they both missed. Renko and his American friend dismiss them knowing they aren't going to get any decent prints off them.
• Subverted deliciously in Feet of Clay by Terry Pratchett. Obviously there are no fingerprint kits on the Discworld, but Vimes makes a point several times of saying that they'll never get any clues off of (object X) since it's full of so many dirty fingerprints.
• In the book The Final Chapter, Officer Denis takes a fingerprint from a piece of string. A fingerprint that was left five years ago. On a piece of string that was holding together a stack of notebooks. Notebooks which, during those five years, got soaked so bad the writing in them has become completely illegible.
• The 'superglue fingerprinting' technique is actually used in one of the Hive stories of the Whateley Universe. But Whateley Academy's security officers don't have to have a case that will hold up in court, since the murderer pissed off a tribe of werewolves by getting one of their allies killed...
• In the novel Digital Knight, fingerprinting turned out to be totally useless because the shapeshifting abilities of werewolves was so accurate as to copy the fingerprints and DNA of the people they imitate. The hero had to invent a special sensor to distinguish werewolves from humans.

Live Action Television

• CSI:
  • Was able to pull DNA from a fingerprint. Another time, someone notes that no one has ever pulled a successful print off an object as small as the one in question, and all the team members look at each other as if to say "A challenge!"
  • They subverted this in one episode - a cleanly lifted print in an old case is shown to be fabricated because there was no way that it could have been lifted from the surface claimed (an alligator-skin wallet).
• One episode of CSI: Miami had an interesting variation; the fingerprints on the weapon matched a rape victim from a previous crime that the tech hadn't deleted. The tech ended up losing her job, and yes, the victim was the new perp.
• Possible aversion: the first episode of Knight Rider had a character mention that fingerprints are not kept on file for anyone who has never been convicted of a crime or employed by the government.
• Law and Order:
  • Played it a bit more realistically in regards to latent prints. The detectives often mention that in processing the crime scene they could only find inconclusive partial prints or dozens that couldn't be identified.
  • In addition, one L&O episode revolved around a fingerprint technician who gave the detectives positive matches by cooking (faking) the evidence.
• NCIS:
  • Averted in an episode where partial prints were run through AFIS and it did come back with something: 80,000 possible matches.
  • In another episode, AFIS was backed up for several days, nearly allowing the criminal to escape.
  • They do manage to "rehydrate" a burned corpse to retrieve prints.
  • Ducky once claimed they had gathered evidence like this, and relied on The CSI Effect to trick the suspect.
• The Closer: Varies as the plot requires. In one memorable episode, they actually sluff the skin off the corpse's hand in order to get a print. In order to use the glove-like skin, they have to slide it over Chief Johnson's hand. This actually works.
• In a possibly literal example of this trope, Star Trek Voyager had the crew use "Displaced Photons" to determine who was telepathically attacking the Maquis crew members.
  • In an even more literal example, an episode of Star Trek: The Next Generation had Data track a person's movements through a system of caves by monitoring the displaced air from the person's passage.
• In The Adventures of Brisco County, Jr., the titular character invents fingerprinting. He was able to lift a clean print off of a shell still in the chamber of a Derringer, but the odd thing is that he got a completely identical print from another object.
• Averted in Life On Mars. When Sam is annoyed because a body has been moved before it's been fingerprinted, his 1970's colleagues are bemused because the technology to take fingerprints off skin hasn't been invented yet.
• Subverted in an episode of Numb3rs. They have two potential suspects and a partial print. Charlie is criticizing the forensic technician's methods—how does she know which finger it's from, etc.--and she gets pissed at him and points out that the print has a rare marking that only matches one of the suspects. Then it turns out that the culprit was a third man, who had the same rare marking on one of his fingers.
• One episode of the live-action Zorro show had Zorro invent fingerprinting. He investigates the Alcalde's (Mayor's) office in an episode where the Alcalde is acting strangely: rescinding unpopular decrees one moment, then punishing people for violating the decree they were just told was rescinded the next. He finds two sets of fingerprints in the Alcalde's private office (which he presumably doesn't let other people into), leading him to realize that there are two Alcaldes, eventually leading to a Spot the Imposter moment in a public duel against both Alcaldes. Subversion in that the fingerprints were only used to confirm that there was an imposter, but not to identify the imposter That was done by Zorro pointing out that the real Alcalde had a scar on the back of his wrist from a previous fight with him and cutting the sleeves of both Alcaldes to see which one had the scar.
• House was caught for flooding a part of the hospital from fingerprints lifted off the pieces of paper he shoved into a drain. Because wet paper scraps retain fingerprints, apparently.

Video Games

• In the DS-only parts of the Phoenix Wright Ace Attorney series (i.e. the 5th case of the first game and the 2nd case in the fourth, Apollo Justice) while fingerprints always provide a match, they're not always clear. It also shows in great detail how the fingerprinting process actually happens. On the other hand, most of the cases are "closed universes", so rather than trying to compare prints against everyone in the world, they're only compared against the eight or so people who we already know have ties to the case.
  • On the other hand, you do automagically have fingerprints on file for everyone involved in those cases, even when there's no reason for you to (this is almost justified in the 5th case of the first game, since all the suspects are cops or work for the government -- but there's no real reason why you would have access to those prints on file And you were given the kit by Edgeworth.)
  • But then the game is rather realistic there—in real life fingerprints are usually used to find out which of a group of existing suspects handled an object, rather than (as TV would have you believe) randomly comparing the prints to a whole database full. And in that case you can easily have the suspects fingerprinted at the time of the investigation.
  • And in one of the cases of the third game, a case is broken because Phoenix's fingerprints are on a vital piece of evidence. This is spoiled pretty quickly to anyone looking in the Court Record, as in this part of this case (and nowhere else in the entire game until you change player characters), Phoenix's profile is available to present, so you know you're going to have to. That and you just found said evidence and put your fingerprints all over it in the previous chapter.
• In Persona 4 the police are able to get prints off of cloth, Adachi is amazed at it.

Adachi: Man, isn't crime scene investigation something? Who would've thought you could get viable prints from cloth

• Subverted by Inside Man, where they find many fingerprints, but quickly realize that all any of them prove is that the dozens of suspects were all at the bank that day.
• Averted in Mass Effect 2, when Shepard and Kasumi have to thoroughly search to find a useable DNA sample from their target's own bedroom.

Western Animation

• Possibly parodied in an episode of the 1980s Teenage Mutant Ninja Turtles TV series, where a television detective mentions she can get fingerprints off a pizza crust. Even to a child that seemed off somehow.
• Played with in an episode of Gargoyles where Broadway accidentally shoots Eliza with her gun. The police are able to pull a complete set of prints off it, but dismiss them as being "so badly smudged they didn't even look human."

Real Life

• The amount of DNA necessary for a speedy, accurate and legally admissible DNA profile of a human being is the amount contained in 120 recently living cells. One-hundred-and-twenty! The only reason it takes a few days to get a DNA profile in real life from any self-respecting and law abiding forensic laboratory is because the scientists have to critically evaluate the significance of the tissue sample and how and where it was found and sampled. Thus, saliva from, say-licking an envelope-is more than enough to get a legally admissible identification. Also, the FBI patented a brand of paper that stores DNA samples for at least 14 years without degrading the sample, quite some time ago.
• Most cases where fingerprints are found on guns. There's some dispute about how often fingerprints are found on firearms or ammunition (see this paper for a study finding fingerprints on only 93 of 1,000 firearms tested). Examiners have testified in other cases about finding usable prints on between 5% and 50% of recovered firearms, depending on how they were handled at the crime scene.
• There is also a chance that your perpetrator doesn't have fingerprints at all. Plenty of people have been in burn accidents and certain medical patients lose their fingerprints through treatments.
• Real Life example: In October 2007, the FBI announced that it had obtained a partial DNA profile of D.B. Cooper, who hijacked a plane in 1971 and left his necktie behind. Apparently, they managed to get DNA off it after all these years (and somehow determine that it came only from him, and not a fellow passenger's dandruff flakes that fell on it).
• There actually is a Real Life Fingerprint database, which everyone and anyone trying to enlist in the US military must give prints for. The list is massive (millions of prints), and is probably what was referenced by the NCIS database matches. This is actually saved for uses of identification, due to the many things that may happen to a soldier, Marine, airman or sailor. Whether or not it's used for criminal cases is unknown, but likely.^{[please verify]}
  • The interesting thing is, once a person leaves the military properly (not AWOL or Dishonorable Discharge) they can submit a request that this and any DNA information the government stores of them to be destroyed since it is contractually the person's property. And on another note, most of the fingerprint information is still kept in card files with much left to be digitized because it is seen as more secure.
• The largest fingerprint and DNA database is maintained by the UK Government; anyone who is arrested or comes into official contact with the police is fingerprinted and has their DNA stored, and these are kept permanently regardless of whether any crime was committed. Some police forces (but not all) also take biometric data from schoolchildren, which has attracted criticism. On the flip side, there have been campaigns for biometric data for children in the event of abduction.