The Substitute 2: School's Out

When his brother Randall is murdered in a carjacking gone wrong, mercenary Karl Thomasson (Treat Williams) goes undercover at his brother's high school to find out who killed him. He learns that a fellow teacher, Warren Drummond (B.D. Wong) is the leader of a car theft ring "The Brotherhood" that had Randall killed when he was getting too close to the truth. Drummond also kills Kara Levelle (Michael Michele) when she also gets too close.

The actual killer of Randall is Anya Thomasson's (Susan May Pratt) boyfriend Danny who killed her father for an initiation into the Brotherhood gang. Anya beats him up upon learning the truth and Drummond later confesses indirectly to murdering him (off-screen).

Thomasson confronts Drummond about Levelle's murder and they fight, ending with Thomasson stabbing Drummond to death with a screwdriver. Thomasson and Anya pay their respects at Randall's grave. While Anya offers him a chance to stay at her home, Thomasson declines, and heads off for another job now that his brother has been avenged.

Thanks Spectre!