Decided to dig a bit, and found that he wrote the
Dark Alliance book/articles, which detail the whole CIA/drug lord connection.
Most of the criticisms against it were that the proof he sets out in his book is shaky. No cross-referencing with other sources, for example. As I understand it, it's quite likely that the CIA was not directly involved, but rather turned a blind eye to the drug smugglers funding Nicaraguan Contra groups.
His death was indeed ruled a suicide, with two gunshot wounds in his head. The coroner claimed that it was "unusual", but also "a distinct possibility". According to the report, the first shot entered from in front of his ear, and exited through his jaw on the other end, going through the lower half of his face. I can imagine a shot like that missing all the vital parts of a head. The second shot reportedly hit an artery, which killed him.
His ex-wife claimed that she believed it was suicide. She claimed Webb was depressed, unable to find a new job, and was in financial ruin. He was also homeless at that point.
Could it be retaliation? Maybe. But his death was 8 years after the publication of his Dark Alliance book. If it
was a hit, and not suicide, it would make sense that it happened earlier. 8 years seems like an oddly long time to wait to take out an annoying reporter.
So, were there shady things going on between the CIA and Nicaraguan drug runners? Not directly, I don't think. I think they just let them be, didn't intervene, and so indirectly helped them.
Was he assassinated for his exposé? I don't think so either. I think he was pushed to the edge. Either through a slander campaign organized by the CIA, or by his own shaky practices and controversies, which caused him to be unable to hold a job. In either case, not an unlikely situation for someone to end their own life. The double headshot is... also not impossible, I suppose. Improbable, but I can imagine someone screwing up like that.