Federal authorities are seeking to heat up a cold trail to a notorious fugitive who has spent the last 25 years on the FBI’s Ten Most Wanted List.

The FBI has increased its reward for information leading to the arrest of Donald Eugene Webb, or the whereabouts of his remains, to $100,000. Webb, if still alive, is believed to be 84.

Webb has been on the run since 1980 after shooting and killing the police chief of a small Pennsylvania town. He specialized in jewelry store robberies and was a career criminal with the mob. He was living in New Bedford, but investigators believe he was in Saxonburg to case a jewelry store.

Saxonburg Police Chief Gregory Adams pulled Webb over on Dec. 4, 1980 after he ran a red light, Gordon Mainhart told the Associated Press. Mainhart was the only other police officer in town at the time. Webb's rental car and Adams' cruiser were seen in the parking lot of an Agway store. A neighbor called 911 after her son heard gunshots.

Adams had been shot twice in the chest and was found lying in some bushes.

"It didn't make any sense," said Mainhart, who rode in the ambulance with Adams. He died on the way to the hospital.

"I was devastated — just a feeling of why? And how could this happen?" Mainhart said.

A fake driver’s license was left behind at the scene and authorities figured out his identity from there. The identification was in the name of Stanley Portas, the late husband of Webb’s wife, Lillian. It was an alias Webb has been using at the time.

Webb's car was later found abandoned in the parking lot of a Howard Johnson's restaurant in Warwick, Rhode Island. Authorities found Webb's blood on the driver's-side floorboard, confirming suspicion that he'd been wounded during the struggle with Adams.

The last time Webb was scene was in Miami 18 months later. After that, the trail went cold.

The only other leads the FBI had were theories, including that Webb was killed by members of the Patriarca crime family. Webb was a member of a group of criminals in southeastern Massachusetts known as the Fall River Gang. Authorities believe the gang sold stolen jewelry through the Patriarca family. However, key investigators believe Webb is still alive – even at his old age.

"The guy is a career criminal. He knows how the system works. There's a good possibility that he assumed another name and has hidden out there all these years," said James Poydence, a retired detective with the Pennsylvania State Police.

FBI Special Agent Thomas MacDonald said he believes Webb shot Adams because he knew police would learn he was wanted for a burglary in New York and he'd end up back in prison.

Adams' widow, Mary Ann — left with two young sons to raise — remarried and rebuilt her life but still longs to know what happened in the moments before her husband's death.

"If he's dead, fine, then God will deal with him. But if he's not dead, I would like to see him prosecuted," she said.

Webb is considered to be extremely dangerous and a master of “assumed identities.” The wanted report on him says he is a lover of dogs, a flashy dresser, a big tipper and reportedly allergic to penicillin.

He also may have tattoos that say “DON” on his right hand and “ANN” on his chest.

The FBI urges anyone with information about Webb to contact their local FBI field office of American Embassy or Consulate.

The Associated Press contributed to this report.