Or, and I put this forward without malice, a drug overdose might simply be a drug overdose.

I'm not saying that there isn't a massive child abuse problem there, it wouldn't shock me to find such rings existing world wide.

What I'm saying is that "Trying to help the street kids" isn't worth the risk of killing even a nobody. A few sandwiches and funding for a shelter for runaways isn't enough for that at all. The only reason they'd take that kind of risk would be if the threat posed was huge.

I doubt that this man was going to take down a child kidnapping ring by himself.

Not to be mean, but I've found most drug addicts to be selfish people at heart anyway, so it would have been easier to wait and let him get bored and lose interest anyway.

Now, none of this means that he wasn't murdered, but I actually doubt it, based on the reasoning given in the OP. There just wouldn't be enough pay off in it for anyone.