I just watched the movie Collateral. I understand about everyone's role in the movie but I don't know what motivates Vincent to kill the 5 people. What is/are the reason(s) behind this? Is there any information regarding contracts on other people (that are killed) or the person that gave the contract to Vincent? Is Vincent killing people because he wants the world to notice him?
Vincent is a contract killer; he is killing them because he's paid to. He was hired by "drug lord Felix Reyes-Torrena", as the Wikipedia synopsis explains:
FBI special agent Frank Pedrosa... identifies the targets as witnesses in a federal grand jury indicting Felix tomorrow. In retaliation, Felix has hired Vincent to kill all five key witnesses.
Vincent is hoping that the world doesn't notice him, hence the (previously-successful) attempt to pin the murders on his cab driver.