As a reporter for the Boston Globe, Dick Lehr began covering the Boston mob boss James (Whitey) Bulger in 1988. In 2000 he coauthored Black Mass: Whitey Bulger, the FBI, and a Devil’s Deal, with Gerard O’Neill. And this week he saw the fruits of his labors transformed into a major motion picture of the same name, starring Johnny Depp as Whitey Bulger.

The movie premiered at Coolidge Corner Theatre in Boston on Tuesday, and the night before at the Toronto International Film Festival.

Like the book, the film follows the years of Mr. Bulger’s involvement as an informant for the FBI, and the corruption of FBI agents, specifically John Connolly. Following the Boston premiere, Mr. Lehr, a seasonal resident of Aquinnah, told the Gazette he was pleased with the adaptation.

“It’s kind of surreal, it’s journalism that I worked hard on . . . to see it on the big screen, I’d never seen that before,” Mr. Lehr said.

Johnny Depp, who portrayed Whitey in the film, at the Boston premiere. — Barry Chin/Boston Globe

Mr. Lehr called the journey to the big screen a typical Hollywood process, with zigs and zags in cast and crew.

The book was first optioned by Harvey Weinstein even before it was published, for what was then Miramax Films. Mr. Weinstein had produced Good Will Hunting a few years before, starring Matt Damon and Ben Affleck, and originally had those two actors in mind to play the starring roles.

In 2006, Brian Oliver took over the movie rights. Johnny Depp became involved with the film in 2013, officially signing on to play Mr. Bulger the next year. Mr. Lehr said he watched the development process mostly from the sidelines, and did not have much control over how the book was adapted for the screen. However, his expertise on the subject was brought into play on set.

During the filming of a murder scene in a South Boston apartment, Mr. Lehr noted that gangster Kevin Weeks was missing from the scene, though he was present in real life. He mentioned that Mr. Weeks had been present, and this revelation led to a meeting with the producer and Johnny Depp to discuss the scene. After talking it over, they decided they needed Mr. Weeks in the scene, and sent for actor Jesse Plemons.

“I’m an observer, it was an important thing to point out, and they responded to it,” Mr. Lehr said. “It was a really important scene, they wanted to preserve the accuracy. If they change the time of a murder to 10 p.m. instead of midnight, it doesn’t matter, but that’s a big deal, a substantive departure from the facts.”

Though the two hour movie had to make cuts and modifications for pacing reasons, Mr. Lehr said the essence of the story remained.

“That, to me, is huge,” he said. “I would not be happy if they decided to turn Whitey into a dark hero, a Robin Hood figure. He is a dark and horrifying force in this movie and that is accurate.”

Although the film accurately focuses on the human relationships between the FBI and the gangsters, with agents Mr. Connolly and John Morris, and gangsters Mr. Bulger and Steve Flemmi, Mr. Lehr said that he would have liked the story to have included more about corruption in the FBI, an essential element in the life of Whitey Bulger.

“This isn’t a couple of local cops, it’s the nation’s top law enforcement agency,” he said. “That’s a big piece of the story and should not be forgotten.”

Although he tried many times to speak directly with Mr. Bulger during his many years of reporting and writing about him, Mr. Lehr was never granted an audience with the mobster. Neither was Johnny Depp, who also tried to reach out to Mr. Bulger while researching his character.

Mr. Lehr said that despite this, Mr. Depp’s portrayal was very accurate, on all levels.

“I thought it was spot on,” he said. “[Mr. Depp] captured him physically, his tucked-in rage, he could kill you.”

Mr. Lehr added that he thought the acting across the board was accurate. Actor Marc Carver played Mr. Lehr in the film and Richard Donnelly played coauthor Mr. O’Neill.

Three additional books by Mr. Lehr are in currently in production. The Fence and Judgement Ridge are slated to become motion pictures, while A Birth of a Nation is in the works as a PBS documentary.

Mr. Lehr said he has been to movie premieres before, but this was the first one for something he had worked on.

“It was a spectacle, it was bizarre,” he said. Mr. Lehr attended with his family, after returning from the premiere at the Toronto International Film Festival the night before.

Black Mass opened on the Vineyard Thursday night at Edgartown Cinemas, and will be playing throughout the week at various locations.