NORTH DARTMOUTH - The longest-running cold case involving a police officer in American history brings FBI agents to North Dartmouth.

In 1980, Saxonburg, Pennsylvania Police Chief Gregory Adams was conducting a traffic stop when he was shot twice and pistol-whipped to death with his own service weapon. Police say the suspect, Donald Eugene Webb, disappeared after the murder.

WPXI-TV in Pittsburgh reports FBI agents investigating the case have been searching a Maplecrest Drive, Dartmouth home belonging to Webb's wife in recent months.

Tom King, attorney for the Adams family, tells WPXI-TV agents discovered a secret room hidden behind a closet, and a cane that's believed to be Donald Webb's which could firmly link him to the murder. "The new information that the FBI has updated the family with, which leads us to believe that we have now discovered the link with the [Webb] family, the secret room that was found up in Massachusetts, and we're hoping that that's what we can accomplish," said King.

Webb is believed to have been shot in the leg during the confrontation with Chief Adams.

Attorney King has filed a civil suit on behalf of the Adams family against Webb's wife and son in hopes of forcing them to relinquish information on the case, and possibly Webb's whereabouts.

"We're going to hopefully get an order that will be enforcable in Massachusetts, and we're going to bring these families up there to the table and we're going to ask them the questions, the hard questions, that will hopefully reveal where Donald Eugene Webb is."

The FBI is currently offering a $100,000 reward for information leading to Webb's capture.