More than 40 years after police officer Matthew Murphy was shot and killed during a traffic stop in Alice, TX, investigators believe they have found the person responsible.

According to an Oct. 24 affidavit filed by Sgt. Aniceto Perez Jr., Alice police identified 70-year-old Roberto Lopez — an inmate who was being held at the St. Clair Correctional Facility in Springville, AL — as a suspect in Murphy's death. Lopez is accused of fatally shooting Murphy in December 1974 after an early morning traffic stop near the intersection of U.S. Highway 281 and West Main Street.

Jail officials in Alabama told the Caller Lopez was a prisoner serving a life sentence without parole, but did not provide additional details. An arrest warrant was later issued for Lopez's arrest, but he was not in the Jim Wells County Jail as of Thursday afternoon, Sheriff Danny Bueno said.

According to the affidavit, Lopez reportedly bragged while in prison about shooting and killing a "narc" named "Murphy" with a .22-caliber pistol. Murphy was an undercover narcotics agent who had been put back on patrol at the time of his death. He was shot several times and later died at a nearby hospital.