7:46 p.m. Thursday, July 22, 2010A former Polk County police officer accused of trying to protect friends he knew were involved in criminal activity was convicted Thursday in federal court.

Mark Howell Sparks, 40, was convicted of witness tampering, obstruction of justice and possession of a motor vehicle with an altered vehicle identification number, according to the U.S. Attorney’s Office.

Sparks resigned from the Polk County police department following his Oct. 6 arrest. At the time of his arrest, Sparks confessed to driving a truck he knew was stolen and had an altered VIN number, U.S. Attorney Sally Quillian Yates said.

Sparks was a detective during an investigation into a suspected chop shop, and knew several of the individuals targeted in the investigation, according to prosecutors. The former cop allegedly tipped off an individual that a search warrant would be executed, and also withheld information regarding illegal activity, Yates’ office said.

Sparks could be sentenced to up to 10 years in prison. His sentencing is scheduled for October.