That Secret Sunday (1986)

Four off-duty police officers party with two sisters. When one dies of a drug overdose, the other one is accidentally killed by the foursome as they try to prevent her from running for help. They hide the body of the second girl and then plant the first girl's body in a shopping mall to make it look like the work of a serial killer, who had been murdering local woman. The only problem, an investigative reporter (James Farentino) doesn't believe the setup and is convinced the murder is a copy cat. He launches a team of reporters to investigate the killings.