BOSTON — Investigators who spent years building a criminal case against gangster James “Whitey” Bulger have long believed he had multiple helpers when he fled Boston and went on the run.

But if prosecutors don’t bring charges within the next few months, the only person to be charged with actually assisting the notorious crime boss during his 16 years as a fugitive will be his longtime girlfriend.

The statute of limitations for harboring a fugitive is five years. The clock began ticking when Bulger was captured in Santa Monica, California, on June 22, 2011, and runs out on June 22, 2016.

Catherine Greig, who accompanied Bulger on his long flight from justice, was sentenced to eight years in prison for helping him.

Greig faces additional prison time after pleading guilty last month to contempt for refusing to testify before a grand jury investigating who else may have helped Bulger.

Now the question is, without Greig’s help, will anyone else ever be charged?

“I don’t think the chances are great. I’d be happy to see it, but I’d be surprised to see it,” said retired state police Col. Thomas Foley, who spent two decades pursuing Bulger.

Bulger, now 86, is serving a life sentence after being convicted of a litany of crimes during a 2013 racketeering trial, including participating in 11 murders.

Over the years, investigators suspected Bulger received help from his family, and attention focused on his brother, William Bulger, a powerful political figure who was president of the state Senate for 17 years.

But William Bulger has denied helping his brother while he was a fugitive and has never been charged. In testimony before a federal grand jury in 2001, William Bulger acknowledged that he and his brother spoke by phone shortly after he fled Boston in late 1994. William Bulger also acknowledged that he did not encourage his brother to surrender.

“I don’t feel an obligation to help everyone catch him,” he said, according to leaked transcripts of testimony published in The Boston Globe.

Another brother, John “Jackie” Bulger, pleaded guilty to perjury and obstruction of justice in 2003 for lying to federal grand juries. Jackie Bulger admitted he had spoken to his brother while he was a fugitive. He also admitted lying when he testified he had no knowledge about a safe deposit box owned by his brother.

Greig’s twin sister, Margaret McCusker, pleaded guilty to lying to a grand jury about having contact with her sister after she fled Boston with Bulger.

Kevin Weeks, a key Bulger henchman, admitted that he provided Bulger with fake identification while he was on the run. Weeks served five years in prison for being an accessory to five murders, but was not charged with helping Bulger as a fugitive.

Another key question: Where is the money Bulger hid? The FBI seized cash from safe deposit boxes in Florida, London, Canada and Ireland. But investigators believe that was just a fraction of the money Bulger made through his gang’s illegtal activities.