Four years have passed since bombs went off at the finish line of the Boston Marathon that turned then-27-year old Jeff Bauman into a double amputee. In that time, Bauman’s inspiring story – which for many symbolizes Boston’s strength in bouncing back from the tragedy – has been captured in a book, which was then adapted into screenplay and now, the movie “Stronger,” starring Jake Gyllenhaal as Bauman.

During that time, Bauman’s recovery – physically, emotionally and mentally – did not happen all at once, nor was it a linear process. In fact, according to Gyllenhaal, Bauman was in a dramatically different headspace at the end of shooting “Stronger” compared to when he saw an early version of the movie.

“In this past year he’s gotten sober, he’s in therapy three times a week and he has conscientiously decided to be a deeply involved father to his daughter,” said Gyllenhaal in an interview with IndieWire.

“He’s turned his life around. He wasn’t there when we wrapped.”

Many films about historical events and figures strive for authenticity. That was certainly how Gyllenhaal started his process of preparing to play Braum – doing extensive research about bilateral amputees, post-traumatic stress disorder and trying to figure how he would balance the internal and external demands of the role. Gyllenhaal told IndieWire that over the last six years he has dedicated himself to embracing multiple acting approaches, exposing himself to the various methods rather than settling for an overarching approach.

“I really thought going into this role I’d be taking all of [what I learned] into playing this guy,” said Gyllenhaal. “Now what I feel is Jeff’s made me see the absurdity of what I do.”

In other words, it didn’t go the way he expected. “Making a movie starts with many different intentions, whether it’s a deep creative need or something more insidious, like the desire to purely make money,” said Gyllenhaal. “But I’ve never been part of a movie that has been a piece of healing.” (In a fairly weak year for the best actor Oscar race, Gyllenhaal’s heartfelt performance stands a good chance of standing out, even though the movie wasn’t a big commercial success.)

According to the Gyllenhaal, there was a risk with Bauman’s story to get overshadowed by the horrific events of the marathon bombing, but the key to the film was finding the constantly evolving and “profound repercussions toward the positive” that stemmed from the explosion and were part of Bauman’s still on-going journey. To tell his story it meant Gyllenhaal and filmmaking team needed to embrace their role of being part of it.

“And the thing about this story was it was begging to be told in the moment,” said Gyllenhaal. “You are doing this in the midst of the complications of the reverberations of the situation.”

It’s for this reason that director David Gordon Green – whose varied career swings between broad comedies (“Pineapple Express”) and naturalistic dramas (“Manglehorn”) – seemed from the outside to be miscast for “Stronger,” but figured out his own way into it.

“David was described to me as ‘the least toxic director’ imaginable, and it’s true, because he’s so insanely collaborative” said Gyllenhaal. “He’s always out having dinner and beers with the entire crew, and has this ‘everybody’s going out to dinner together’ mentality and that’s what it was like with Jeff and everybody involved in this story – they were just coming over for dinner.”

Ultimately, there was still intensely hard work to be done in preparation for the role, and Gyllenhaal said he felt fortunate that Bauman — now a close friend of the actor — put in the hundreds of hours to be by his side, helping him prepare by showing him how he gets around in life. The dramatic scene in which Gyllenhaal, as Bauman, takes his first steps took countless hours of physical preparation. Gyllenhaal started to figure out the challenges of Bauman’s movement in the scene after he got used to feeling confined to a wheelchair.

“Jeff has specific movements, and I started to fall in love with how he moved beyond his injury,” said Gyllenhaal. “The strange idiosyncrasies that he has as a person, there’s almost this innocence to him that I tried to put into my body.”

For an actor who has put so much time into thinking about his process, Gyllenhaal found there to be something so beautiful and organic about making “Stronger” that he expressed genuine uncertainty how he’d approach character preparation for his next film with writer-director Dan Gilroy (“Nightcrawler”) early next year. But he’s aware of one important tool Bauman has gifted him.

“In terms of creating a character, I’ve gained a sense of humor about the process,” said Gyllenhaal. “It was a huge missing element to my process because Jeff just thinks it’s absurd, but yet he loved making this movie.”