Glaring plot hole *SPOILER ALERT*
OK so after Luke is captured, Markus wanted him dead in fear of him exposing him after the harsh conditions of prison. Although this seemed pretty inhumane after Luke's loyal service and the fact that he didn't snitch on him after being captured, it's still understandable from a business perspective.
However, why did he still try to get Luke killed, even with more urgency than before, when he was entered into the Death Race and was winning? Surely, since the winner wins his freedom, he should wait and see if he will win, and perhaps even helping him win by targeting the other racers? Even if he doesn't do this, he could at least wait and see if someone else will take Luke out anyways and save his million bucks?
If Luke really was like a brother to him then his actions here simply doesn't make sense. Buuuuut in the end I guess the plot doesn't matter in a movie like this...