AceShowbiz - Judd Apatow and his "The King of Staten Island" cast realised they'd struck gold by landing former firefighter Steve Buscemi for the film, because he brought such authenticity to the set.

The movie, a semi-biography of comedian Pete Davidson's life, deals with a lost 20-something trying to come to terms with the death of his fireman father, and Buscemi plays a veteran firefighter.

The stars of the film and Apatow knew they were making magic when Buscemi was on set for firehouse scenes, because he served as a firefighter in New York in the 1980s and he returned to volunteer with the force after the 9/11 terrorist attacks on the Big Apple.

Comedian Bill Burr, who also portrays a fireman in the film, says, "You know when you're watching a pro. The way Steve did it, the muscle memory was there."

Davidson adds, "Steve crushed it, and the fact that he was also a fireman made it special. That man is so sweet he makes me cry looking at his face."

And director Apatow insists the "Reservoir Dogs" star "was not acting, he was venting".

Burr also enjoyed spending time at a real fire station, hanging out with film consultant John Sorrentino, who was a close friend of Davidson's late father in real life.

"One of the first things we did was go to Pete's dad's firehouse (in Brooklyn Heights)," Bill explains. "That was super emotional. We went downstairs and there was all this 9/11 memorabilia, and I thought about how they had lost so many guys in that firehouse. I remember John Sorrentino going, 'Alright, it's been long enough I can talk about it now'."

"I thought, 'There is no way I'm going to do this justice. Do they realise who they hired?' I was very humbled and nervous."

Davidson's father, Scott, died on 9/11 in 2001 when Pete was only seven.