The Milk star's new crime thriller Gangster Squad became a casualty of the Colorado tragedy as studio bosses at Warner Bros. yanked trailers for the film from cinemas - because footage included a shoot-out at a movie theatre.
Producers then opted to reshoot the scenes, which were filmed at Hollywood's famous Chinese Theatre - and Brolin and his castmates were called back to work.
But that wasn't on Brolin's mind when he first heard of the deaths of 12 movie fans.
He tells Men's Journal magazine, ""I immediately started crying, and the stresses of my life immediately became irrelevant, meaningless confetti.""
And speaking to the publication the day after the massacre for an interview that has appeared in the latest issue, he admits he felt ""a modicum of pain for the perpetrator,"" James Holmes, adding, ""What happened to the kid to put him in that position? Is he truly mentally deranged? Was he born that way?""
A hearing into Holmes' Aurora massacre began in Colorado on Monday (07Jan13) as families of the victims packed the Centennial courthouse to hear details of the case against the alleged gunman.
Police officials and witnesses described the scene in the cinema after the massacre and the ""relaxed"" nature of Holmes following his arrest.
Coincidentally, the Aurora cinema where the shoot-out took place is scheduled to re-open next week (17Jan13).