"The Army has one simple rule... kill or be killed"

The Base 2: Guilty as Charged (2000)

US Army Investigator John Murphy has been sent to look into a series of suspicious deaths that have been going on under the watch of Colonel Strauss. After going undercover and infiltrating Strauss's unit, Murphy discovers that Strauss and his men are leading a vigilante gang to dispense 'justice' to those they feel have been wrongly acquitted of various crimes.