Publicist Scotty Dugan died while en route to the funeral of slain music executive and film producer John Atterberry on Wednesday of as-yet-undetermined causes, TheWrap has confirmed. He was 52.

Dugan was at a Los Angeles County Metropolitan Transit Authority train stop when he was stricken, according to Dugan's client and friend Jennifer Gotzon. An autopsy is pending. Gotzon tells TheWrap a heart attack or brain aneurysm is suspected.

Witnesses saw Dugan clutch his head and complain loudly of head pain.

He just dropped to the ground, Gotzon said.

Dugan was transported to a local hospital, where he was pronounced dead late Wednesday morning.

Dugan had been working on the upcoming film God's Country, which Atterberry had written and produced. Gotzon stars in the movie.

Dugan's family in Boston is making preparations to have his remains transported back east for burial. Plans for a memorial service in Los Angeles, likely during the first weekend of January, are underway, Gotzon told TheWrap.

Dugan was single and had no children.

Dugan's IMDB profile states that he began an early career as a photographer selling pictures to such publications as the Reading Chronicle, the Boston Herald and the Boston Globe. After studying journalism at Boston University, he became employed in the sports department of the Boston Herald, and worked as an editor at the Hollywood Reporter for a period.

Gotzon remembers Dugan as a man who fully immersed himself in the projects he became involved in.

He gave selflessly and poured passion and energy into projects that sometimes nobody even asked him to, Gotzon told TheWrap. He did the work of 10 men in one day ... he had energy that nobody could understand.

Atterberry, a former Death Row Records music executive, was struck multiple times during a shooting rampage at the intersection of Sunset Boulevard and Vine Street in Hollywood on December 9, and died December 12. He was 40.

The assailant, Tyler Brehm, was fatally shot by police. According to police, Brehm was distraught over a recent breakup.