Concerned/WMG

The Vortigaunt killed Frohman because he knew too much.
Why did the vortigaunt leave Frohman to die in the end of the series? Because he shoot them? They are not petty enough for that, besides, they saved Freeman, who has already killed who knows how many of them. Because he is a moron? No, we already know that Freeman himself is not much better. The obvious conclusion is the vortigaunt have been plotting the downfall of the human race all along, and Frohman knew it.

But, did they merely leave him to die? In Half-Life, people dont die when they have one point left, no matter what kind of amusing injuries left them in that state. No doubt it was the work of the vortigaunt. They have been plotting the death of Frohman for long, but in every ocasion there was some nearby humans and they had to keep appearances, even ocasionally saving his life, ironically enough.


 * They saved Freeman because he was totally going to save the rest of the world later

Concerned is canon in the Half-Life universe.
Hence, the Playstation Half-Life is non-canon. It will probably be alluded to in Episode 3. "Generic Rebel 1: "The only thing that could make this situation worse would be if this whole thing was caused by cheese!"
 * Well, that means we either meet Frohman, or we get an exchange along the lines of:

Generic Rebel 2: "...then now would be a bad time to tell you about this guy I met back in City 17.""