(CBS News) In Boston, this is day three of the James "Whitey" Bulger trial. The alleged mob boss is accused of participating in 19 murders. Bulger was arrested two years ago in Santa Monica, Calif. He had been on the run since 1994.
CBS News recently spoke to a neighbor who led the FBI to Bulger.
As far as Josh Bond knew, the elderly man who lived next door in apartment 303 was just a friendly guy who liked to talk. He always identified himself as Charlie Gasko.
"The guy that I knew, I have nothing but good things to say about," Bond said. "He was very nice to me. They were both very kind and generous, supportive -- almost protective."
"Gasko" and the woman he introduced as his wife were Bond's neighbors for five years.
"They seemed, you know, like a retired couple, kinda spending their last years in Santa Monica," said Bond.
But looking back, Bond said he may have missed some red flags.
"He told me he pulled a knife on one of the guys at a guest home down the street," Bond said.
But Bulger's neighbor never suspected anything -- not until the FBI showed up in June of 2011 with pictures of his neighbors on a wanted poster. Bond said he was "pretty shocked" when he saw them.
"Gasko" was actually the notorious fugitive James "Whitey" Bulger, on the run with his girlfriend, Catherine Grieg.
"I went to his Wikipedia page," Bond recalled, "and I'm kinda, like, scrolling through, and it's like, murder and extortion and all this stuff."
"Josh turned out to play a pivotal, central, key role in the capture of Whitey Bulger," explained Dick Lehr, who co-wrote a biography on Bulger.
Bond helped the FBI come up with a plan. He called the couple and told them someone had broken into their basement storage locker.
"Whitey rode the elevator down and walked into the hands of some number of FBI agents and local police with their guns drawn," said Lehr.
After he was arrested, Bond said Bulger "seemed like he was in pretty good spirits."
"To be honest, I mean, he was laughing," recounted Bond. "Seemed like he was jokin' around with some of the agents."
Bond was surprised when he saw what investigators found inside his neighbor's apartment. "I was not expecting, you know, to walk into -- to an apartment full of guns and money."
Since his arrest, Bond said he's received a few letters from Bulger -- letters that he has replied to.
CBS News' Carter Evans asked Bond what they talk about in their exchanges.
"He asked me not to talk about it. So I'm not going to," Bond told CBS News.
Bond will only say that Bulger has forgiven him for helping the FBI and doesn't blame him for his arrest.
Watch Carter Evans' report above.
CBS News legal analyst Rikki Klieman, who is following the Bulger trial, said she's not surprised at all that Bulger has kept in touch with Bond. She said on "CBS This Morning" that Bulger "has this code of honor. You have bad guys and they get in the way, those bad guys we don't want around. But this neighbor was a good guy. This neighbor didn't do anything that any other neighbor wouldn't have done."
For more with Klieman on Bulger, his case and how it's playing out in court, watch her full interview in the player below.