I agree with Damien on "set loose". I don't think that the author is comparing Lehrer and this man, but rather Lehrer is the one who had the ability to set this man loose. In my experience, a "backwater" is not so much a poor area, but rather a little-known area, which receives little attention. I often see a picturesque village described as a "sleepy backwater". I've just checked Merriam Webster and my definition is very similar to theirs (number 2): http://www.merriam-webster.com/dictionary/backwater

It's all very heavy in imagery. "To set loose" is comparing the man to a caged animal and you're setting them free, but they probably mean it in a menacing way. They are purposely freeing the man to do what ever he wanted in "the wild backwaters of the planet," or rather the slums/ghettos/poorer regions of the world. Sooooo..... in general here's my paraphrasing - "He was not a thoughtless murderer, like Lehrer, that could be freed to do all of the killing on behalf of the other guy." Where's this from?

I'm curious too.Is there anyone who can help?