Frontline” begins its 33rd year on Tuesday with a first for PBS’ venerable long-form documentary series. “My Brother’s Bomber,” a search in Libya for those responsible for the 1988 Pan Am Flight 103 bombing over Lockerbie, Scotland, will air in three hour-long installments over the next three weeks.

The expansion into multi-part series is one of many new moves — from experiments with virtual reality to stepped up production of digital content — undertaken by “Frontline” executive producer Raney Aronson-Rath, who has taken the reins of the series this season from her mentor, founding exec producer David Fanning. Aronson-Rath, who joined “Frontline” as a senior producer in 2007, sat down with Variety earlier this month in New York to discuss “Frontline’s” evolution.

From public radio’s “Serial” to HBO’s “The Jinx,” documentary filmmaking is in the midst of a boom and big changes. What prompted you to produce “My Brother’s Bomber” as a multi-part series?

We’re increasingly feeling like our reporting lends itself to these serialized looks at investigations, especially for investigations that are still unfolding. With (‘My Brother’s Bomber’) the investigation took place over so many years and had so many incredible twists and turns. There was so much to tell and so many incredible roads that were taken. It lends itself to three parts that are incredibly dramatic.

Will you offer more documentaries in a multi-part form?

We’re going to see how this format plays for our audience. My assumption is people are going to love it — they can watch for an hour and come back the following week. I’m excited to see how our audience responds to it.

Is it harder to do long-term investigative reporting at a time when the news cycle is 24/7 and virtually everyone has the ability to be a journalist via social media?

We found the appetite for “Frontline” has only grown as the digital landscape has exploded. The appetite for the reporting we do on our digital platforms to the short films we’re doing for our Facebook and YouTube channels. And we’re still producing these remarkable long-form films. There’s an incredible feedback loop between what we can publish iteratively and our films. There are no silos at “Frontline.” Our digital team works with our filmmakers and our filmmakers work with our digital team. They’re always in touch and they’re always talking.

Is it harder to spend years digging on a story before you put anything out?

You won’t see us publishing for publishing’s sake. You’ll see us publishing intentionally and with thought. We don’t rush. I’ve always said you never need to apologize for not publishing; you only need to apologize when you publish too quickly. That’s baked into our DNA. When something goes out with our brand attached to it, you know we’ve thought hard about it. Sometimes that means we publish something a day or two after others but you’ll see a deeper dive from us. You’ll see epiphanies in that work — you’ll see us thinking longer and harder about those things.

Sounds like you are focused on turning “Frontline” into a digital news destination?

“Frontline” started doing digital content in 1995. We started streaming our films in 2000. We established one of the first (Internet) video players because David (Fanning) really believed that our films should be accessible. I have never worried about “Frontline” becoming an old-fashioned news brand because we never were. David was nimble and forward-thinking about digital.

What have you learned about contemporary journalism from expanding your digital activity?

The most profound, life-changing event for me in understanding how we could do cross-platform work was when we started a series in 2009 with ProPublica (news outlet) called “Law & Disorder.” We made the decision then that we should be publishing iteratively with them when the stories were ready. We can publish alongside our partners and it always helps the film in the end anyway.

Our digital numbers are growing exponentially — there’s been a huge uptick in our digital numbers, our mobile numbers and our film streaming numbers. What’s been really inspiring is that new audiences are coming to “Frontline” and they’re telling us to please stay serious, please stay true to the idea of “Frontline” — investigative work that’s done with care and with fairness.

You unveiled “Frontline’s” first virtual-reality documentary, “Ebola Outbreak: A Virtual Journey,” at the Online News Association conference on Sept. 26. Is this the future for docs?

I just completed an MIT (Open Doc Lab) fellowship on the future of journalism. I feel really invigorated by this period of time. The reason is because I see our growth happening and people are hungry for high-quality journalism. I’m seeing younger people engaged and inspired by international affairs in a way that I haven’t seen for a while. I’m seeing people engage with us across all platforms. I feel that the (documentary) world is really growing in a creative sense now that journalists are considering virtual reality and we’re looking at interactive documentaries. I can see us experimenting and innovating with the form. with spherical video, drone photography, virtual reality. One of our film teams took an Oculus camera with them to film the story of Ebola. That’s where I get excited.

How does your commissioning process work? Is it hard to set target dates for films that rely on deep investigative work?

We have 26 original films a year. Twenty are longform films and six are in the magazine format. That has given us a lot of flexibility to do quicker turnaround stories. Like ISIS — we were the first TV organization to have a longform piece on ISIS. We were able to look at the Ebola crisis quickly because we now have the flexibility to do that.

We commission most of our films with filmmakers who have worked with us for quite a long time. We have terrific veteran producers and we have new generation filmmakers work alongside our veteran filmmakers so there’s a multigenerational conversation that happens at ‘Frontline’ that is a very healthy one.

All of this sounds like it takes a lot of resources. How are you doing in terms of funding?

PBS has been incredibly supportive since the beginning of time. Our foundation support has been really strong. That doesn’t mean that we’re not looking constantly at how we can grow our financial base so that we can do even more. The ambition is there to do more all the time but we just want to make sure we’re growing strategically. So far we haven’t become too big yet. We don’t want to dilute our brand. We need to make sure we continue to do high-quality work.

How do you decide what big subjects to take on?

Our feeling is that we need to be saying something really big and really remarkable and something you won’t forget. That’s our special place in the world. … We always start with what do we think editorially and journalistically are the most important stories of our time to tell. We tend to have areas that we have expertise and knowledge in, and we have such a strong base to work from. We don’t tend to do issues — we tend to do stories that have strong narrative and investigative surprises in them. That’s been our method for years.

How do you handle it when a story you’re pursuing doesn’t pan out after you’ve invested a lot of time and money in reporting?

Sometimes stories we want to produce end up (with) a false start but we end up coming back to them. ‘My Brother’s Bomber’ is a great example of that. We had done original research and reporting but then we put it aside because (producer) Ken Dornstein (brother of victim David Dornstein) told us that until he could get into Libya he couldn’t do the original investigation that he wanted to do. So we had to wait until that was possible.

How does it feel to be leading the “Frontline” operation now that founder David Fanning has become executive producer at large?

From all my training with David, the most important thing I got was the understanding of narrative — how do you tell an unforgettable story to get inside the issues of our times. …The really important thing about ‘Frontline’s’ transition is that I had the gift of time. I had multiple years of being mentored by David and a very intensive apprenticeship (starting in 2012). I’ve been groomed for this. It feels very organic and intentional.