Less than a week after being indicted for allegedly tampering with evidence in a homicide investigation, a crime scene investigator is being sued in federal court by one of the men who was wrongfully charged in the double-murder case.

On Sunday, Nicholas Sampson filed paperwork to add David Kofoed, commander of the Douglas County CSI unit, and the Douglas County Sheriff's Office to a 2007 lawsuit filed in U.S. District Court against the Nebraska State Patrol and the Cass County Sheriff's Office.

The amendment says Kofoed violated Sampson's constitutional rights by planting a speck of blood in a car Sampson had driven.

Sampson spent five months in jail after being wrongfully charged in the deaths of Wayne and Sharmon Stock. The couple were found slain in their Cass County farmhouse on April 17, 2006. Both had been shot in the head at close range with a shotgun.

"Law enforcement involved with the Stock investigation insists that the case against Nick Sampson remains an open case," said Sampson's attorney, Maren Chaloupka. "I find that ironic, given that the only person currently under indictment is one of their own."

Kofoed, 52, was charged Wednesday in Cass County Court with evidence tampering and was indicted a day later on four federal charges, including falsifying records.

His attorney, Steve Lefler, has said Kofoed may have made some mistakes in the case, but they did not rise to the level of criminal misconduct.