David Rosenbloom calls them “movie moments,” those ephemeral slivers of magic discovered amongst the voluminous footage he sifts through in his role as an editor. They can be as small as a glance or as large as a cackle from Whitey Bulger.

The latter can be found in Black Mass, Rosenbloom’s second collaboration with director Scott Cooper following 2013’s Out of the Furnace. The film traces the true story of Irish gangster Bulger’s thirty-year reign in Boston, abetted by his role as an FBI informant.

Rosenbloom talked to Filmmaker about his start as an editor, his software of choice for cutting and his work on Black Mass.

Filmmaker: Where did you grow up and how did you fall in love with movies?

Rosenbloom: I grew up in Los Angeles. None of my family was in the film business, although my grandfather was an extra in Wings (1927) and he would take my mother and my uncle down to be extras in things. But nobody actually worked in the film business. I fell in love with movies pretty young. My grandmother would take me and my three brothers to the Dome or theaters in the valley. She took us to all the big event movies — How the West Was Won or The Sound of Music. That was where my love of film began. Then in high school I loved movies like Cool Hand Luke and The Graduate. Cool Hand Luke was probably the first movie I paid money to go back and see a second and a third time.

Filmmaker: How did you get started as an editor?

Rosenbloom: When I was 16 I was offered a job by my best friend’s father, who was vice president and general manager of Hanna-Barbera animation. That first job was called track reading. Before any of the animation they would record all the voices and our job was to very slowly and painstakingly go through the 35mm film of the soundtrack and write down on these long pieces of paper called exposure sheets what foot and what frame the letters fell on so the animators could animate the lips and make it look like (the characters) were talking. It was tedious to say the least, but it was fun for a 16, 17 year old kid. I was making more than $100 a week and it was pretty exciting to me.

Filmmaker: In terms of your career trajectory, how important was the time you spent editing the television show Hill Street Blues in the early ’80s?

Rosenbloom: All the first few movies I did all had some relationship to Hill Street Blues. The first movie I did, Best Seller, was directed by Johnny Flynn, who was a big fan of the show and he hired me based on that and my work cutting the pilot for Miami Vice. Then I did three movies with David Anspaugh, three movies with Mimi Leder and five movies with Gregory Hoblit, all of whom were producers and directors on Hill Street Blues. Rudy was my third film and it was the first movie that was kind of noticed. It didn’t do very well (theatrically), but it’s one of those perennials that people still watch all the time and it got my foot in many doors subsequently.

Filmmaker: It seems like you’ve formed a few long-lasting collaborations with different directors. Black Mass marks your second time working with Scott Cooper following Out of the Furnace. At what point in the process did you become involved in Black Mass?

Rosenbloom: Before we started shooting. Scott had sent me the script a while before and then I was there through the entirety of shooting, which was invaluable I must say.

Filmmaker: Did you go on location for Out of the Furnace?

Rosenbloom: No. Scott and I had only met once when I got that gig and then Scott went off on location. We would talk on the phone every day or every other day, but it was appointment-driven phone calls. The calls were kind of perfunctory. But once he came back to LA and we worked for the next nine months together (cutting the film), we became very close. He saw how I worked and he said, “There’s just no way you won’t come on location on anything else I do.”

It used to be that it was never even a question. The editor was always on location because there was no other way to view dailies without the editing crew. Now, it’s not as necessary and producers and studios look at it as a line item to scrutinize, because it’s money that doesn’t have to be spent. It’s not a huge expense to take an editing crew on location, but there is an expense to house them, pay a per diem, and move the equipment from one part of the country to another.

Filmmaker: During principal photography, are you mainly just putting together an assembly or are you doing fine cuts of scenes as well?

Rosenbloom: It depends on the director. I’ve worked with directors who want to get meticulous and really fine cut stuff while they’re in the process of still shooting, but I feel like the wiser choice is not to do that. As a director, you want to focus on your future, not so much on the past. You want to really be thinking about what you’re going to do the next day and what you’re going to be doing next week. With editing, you spend months and months and months going over the same stuff, but when you’re in production, the director has to get it when (he or she) can get it and I’m aware of that. So if I have something that I really want Scott to hear, he knows that it’s important. And even if it only happens once or twice a month, you’ve absolutely saved yourself hundreds of thousands of dollars if you can head off the need to come back and reshoot something or shoot an additional scene. It’s vital and it proved really important on Black Mass.

Filmmaker: Is it hard to find the rhythm of a scene in these early stages when you don’t have a score or any foley?

Rosenbloom: I don’t need that to cut, but I do need it most of the time to present and that’s just the way it is nowadays. I would say 75 percent of directors would have a hard time looking at a scene without it being all dressed up. 30 years ago I’d put together a scene with scratches and splices jumping and it wouldn’t faze a director. But if you ran that for a director now, my god, they would be beside themselves. I used to run (scenes) through a Moviola with one piece of sound and that’s how the director would watch the film – on a six-inch diagonal screen.

Filmmaker: Is there anything you miss about cutting on film?

Rosenbloom: Once upon a time I did, but now, creatively, I feel like I haven’t given up anything (by editing digitally). When I was first making the transition — and I was really vocal about it to anybody that would listen, because I thought it was a bad thing — I was hesitant because it rushed the process. You now had this ability to immediately put something together and you didn’t give it the same consideration. When you’re cutting on film — physically laying a blade to 35mm film — you really thought about it because to undo it was a big deal. So you considered things more and you really thought it out. You knew where you were going to be in three or four cuts, or at least you thought you knew where you were going to be. And then when you had this opportunity to immediately start cutting without concern for having to uncut it, we all went crazy. We started doing things really quickly without the same sort of consideration. Then the pendulum swung back to a more reasoned approach and I now approach a scene very much the same way I used to on film.

Filmmaker: What is your preferred editing software?

Rosenbloom: Avid.

Filmmaker: Have you tried others?

Rosenbloom: The first picture I (edited) electronically was with a Lightworks system I used on Primal Fear. And then I went back to film on The Peacemaker in 1996, which was the first movie for Steven Spielberg’s company DreamWorks. We were shooting in Eastern Europe and the support there in the mid-90s for digital editing was sketchy, so I was game for going back to film. But that was the last film I cut on film. My next project, Deep Impact, I cut on Avid. I only cut one film on Final Cut — another picture for DreamWorks in 2002 called Dreamer with Kurt Russell and Dakota Fanning about horse racing. Marty Cohen, the head of post at DreamWorks at the time, was very forward thinking and he said, “Final Cut is really trying to create inroads into the feature editing world. Will you try it?” And I said, “Sure, I’ll give it a go.” I hated it. It was cumbersome and not good for moving massive amounts of media around, so since then I’ve been using Avid.

Filmmaker: Black Mass clocks in at just over two hours, which is relatively trim for a gangster epic covering multiple decades. How difficult was it to get the film down to that length?

Rosenbloom: I think the first cut was around two hours and 45 minutes and we really didn’t cut many events out when we brought the (running time) down. Earlier cuts were a little more languid. In the end, the movie is all about characters. It’s not so much about plot. There were never any scenes of Whitey almost getting caught. There wasn’t really anything where you were leaning forward to see where the plot was going to take you. You were just leaning forward to see what these characters were going to do next. How is Whitey going to behave?

Filmmaker: Black Mass uses a framing device in which members of Whitey’s crew recount the events while under interrogation. Was that device in the original script?

Rosenbloom: Initially in the script it was just (the character of) Kevin Weeks being interrogated. We were going to shoot those scenes on the last two days of the schedule, but about halfway through production we had to go to our cover set and that was our cover set. We hadn’t done sufficient tests on Kevin Weeks’ old-age make-up and everything was rushed. As soon as Scott started shooting it, he knew that he was going to re-shoot it all because he wasn’t happy with the make-up and Jesse Plemons (who plays Weeks) was caught unawares because it was such a last-minute thing. I got the film the next day and I placed a couple of those interrogation scenes into where they were scripted and then I brought Scott in. It was one of the few times that we actually sat down with the notion that we had a problem that needed fixing.

The character of Kevin Weeks starts out strong, but he has a lesser and lesser role throughout the story. What we realized as we were sitting there looking at it was, if we’re telling the whole story through Kevin’s point of view, we’re (disproportionately) propping up his prominence in the film. He wasn’t Whitey’s right-hand guy. So we said, “What if we (add interrogation scenes of) Martorano (W. Earl Brown) and Flemmi (Rory Cochrane)?” Now our framing device became not just a singular point of view.

Filmmaker: There are two key scenes for humanizing Whitey Bulger — both set around a kitchen table. The first finds Whitey giving his son some questionable parental advice. The second features Whitey playing gin with his mom. Why are those scenes important to the film?

Rosenbloom: They’re important to the story because they give a little glimpse behind the curtain of who Whitey is. It gave him a human dimension. And also they inject a little bit of humor. Whitey Bulger was a charismatic guy. Nobody has that kind of power or sway over people if they don’t have some charisma.

Filmmaker: Charismatic, but also terrifying. There’s a great scene where Depp puts the screws to an FBI agent over dinner after the agent discloses his family recipe for marinating steak.

Rosenbloom: There are moments that strike you, that for me as an editor I see as a kernel of greatness in a scene. In Out of the Furnace there’s a moment in the scene on the bridge (where Zoe Saldana’s character tells Christian Bale she’s pregnant) where (Saldana) holds the back of her hand to her mouth to try to stop from crying. And she did that in one take. When I saw it I said, “This is magic. This is a movie moment.” It was just a brilliant piece of performance and I knew that it was going to be the focal point of how I was going to approach the scene. Everything led to that and everything led away from that. It was the fulcrum.

Similarly, with the steak dinner scene, I felt that the crux of the scene was the very long beat on (Joel Edgerton’s FBI cohort) John Morris, where it’s just silent before this cackle from Whitey. And then I built the scene out from there. I made everything lead up to it and everything lead away from it. The longer you wait on something, the audience starts to feel less and less comfortable and then rather than break (the tension) with a cut to Johnny starting to laugh, I felt the way to do it was to feel it happen as Morris is feeling it happen.

Matt Mulcahey writes about film on his blog Deep Fried Movies.