Nicky Katt, who played teacher Harry Senate on “Boston Public” after starting as a child actor and going on to play an assortment of tough guys in movies including “Dazed and Confused” and “Boiler Room,” died April 8 in Burbank. He was 54.

The Los Angeles medical examiner’s office reported that the cause of death was suicide.

His death was reported by his friends and by attorney John Sloss.

Often playing heavies and villains, Katt worked with Richard Linklater, appearing in “Waking Life,” “SubUrbia” and “School of Rock.” For director Steven Soderbergh, he appeared in “The Limey” as Stacy the Hitman, as Hitler in “Full Frontal,” and had one of his final roles in “Behind the Candelabra.” Christopher Nolan cast him in “Insomnia” and “The Dark Knight,” in which he played a S.W.A.T. team member.

On “Boston Public,” Katt played the popular geology teacher Harry Senate, who taught troublemaker kinds in “the dungeon.