Harris Laskaway

A young hustler tries to get drug money by selling a boy to a middle-aged man; his plans are disrupted when the kid dies. (imdb)

Follows a cunning hit-man who painstakingly selects his clients and victims. He then commits the murder without the "beneficiary's" knowledge and sends them an invoice for $100,00, with a threat that nonpayment will result in being framed for the murder. (Amazon.com)