Irish American cop Neil Sullivan, a 37-year-old federal marshal, is the man credited with cracking the 'Whitey' Bulger case, according to reports.

Sullivan, a 37-year old marshal, was on the Bulger task force for only seven months when he made the vital breakthrough.

He is credited with going through hundreds of tips and focusing on the one that led to Bulger’s whereabouts.

The key tip was originally phoned in by a woman in Iceland who knew an elderly couple called the Gaskos in Santa Monica, who looked like Bulger and his girlfriend Catherine Greig.

“There was a stack of tips that came in,” a source told the Boston Herald. “He picked one out that he thought was the most legitimate and said they needed to prioritize it.”

“The marshals were key to breaking the case,”  one veteran law-enforcement official who worked on the case for years said.

Sullivan joined the Bulger task force just seven months ago and immediately followed up every lead including traveling to Florida.

“He went running with these things,” the federal source said. “He was traveling around the country interviewing people.”

It has also turned out that Bulger made frequent trips to Mexico to pick up a prescription heart drug and also keep safety boxes in banks in Europe, including in Ireland.

Bulger has been speaking openly to FBI agents since he was arrested and even waived the need for a search warrant to search his Santa Monica apartment.

In the apartment, the agents found a false wall behind which Bulger had stashed guns and vast quantities of money.

The search also found some workout equipment, leading to speculation that fears about Bulger’s health were exaggerated.

He told the FBI he often crossed over the Mexican border to Tijuana, where he brought the prescription drugs that are freely available there.

He sued a false identity to cross over and was never detected despite an FBI focus on cross border efforts based on a hunch that Bulger was seeking medication in Mexico.

FBI officials also found a family connection, Mary Hurley, daughter of Bulger’s brother William, a Masachussetts politician, once lived just two miles away from Bulger.