WMG / Sorcerer

Nilo was hired to kill Jackie.

It seems odd that Nilo would just come into town on some layover and decide to stay there without any explanation. The best explanation would be that he was there on the job and that he may have been hired by the gang that's after Jackie. This explains why he not only tried out for the job, but also why killed Marquez in order to go on the job. Maybe he was trying to get the job not for the money, but to be able to be alone with his target (plus, the truck's route provides plenty of places for privacy to kill Jackie and dump his body without anyone asking questions). Also, maybe the reason why he didn't kill Jackie when he had plenty of chances is because, being a professional himself, he admires Jackie's dedication to the job (in some edits of the film, when Jackie asks Nilo why he killed Marquez, Nilo explains he flipped a coin. When Jackie asks if Marquez lost, his reply is "No. You did. But I'm partial to Americans."). Nilo allowed Jackie to live because that admiration.