PBS’ venerable documentary franchise “Frontline” is expanding into multi-part investigative series, exec producer Raney Aronson told reporters Sunday during PBS’ portion of the Television Critics Assn. press tour.

“Frontline” has a three-part series, “My Brother’s Bomber,” bowing Sept. 29. The series revisits the 1988 bombing of Pan Am Flight 103 over Scotland by following the Ken Dornstein, the brother of victim David Dornstein, on a five-year trek through the Middle East in search of details and clues about the bombing that killed 270 passengers. The hunt was sparked after the only person convicted of the crime, Abdelbaset al-Megrahi, was released from a Scottish jail in 2009. (He died three years later in Libya.)

Aronson, who took the reins of “Frontline” from founding exec producer David Fanning in May, said the Boston-based operation has several large-scale investigations in the works that will be presented as multi-part series in the coming years. She said it was impossible to ignore the recent of deeply reported docu-serials such as public radio’s “Serial” and HBO’s “The Jinx: The Life and Deaths of Robert Durst.”

“Frontline” is looking at options for “telling new stories in different ways,” Aronson told Variety. She would not elaborate on the nature of the investigative reports that are brewing.

In “My Brother’s Bomber,” Dornstein pursued new leads and some information was passed on to U.S. law enforcement. Among those interviewed for the series is former Lockerbie investigator Richard Marquise, a retired FBI Special Agent. But the series “has been a work of journalism,” said Dornstein, a writer and filmmaker who previously worked for “Frontline.”

(Pictured: Raney Aronson, Richard Marquise, Ken Dornstein)