COBBLE HILL, Brooklyn — A Brooklyn man was arrested Wednesday after officers found bomb making materials and guns inside his apartment, law enforcement sources said.

Officers investigating a past burglary knocked on Christopher Hackett’s Butler Street door and noticed three shell casings on the steps when Hackett answered, sources said.

Hackett invited them inside and the officers noticed a gun in plain view during questioning, sources said.

Police arrested Hackett, 44, and a search warrant revealed a makeshift gun and suitcase containing wires, pipes and blue chemicals which the NYPD Bomb Squad later deemed safe, police sources said.

He told detectives he was “trying to make a bomb to show how easy it is to walk around with one,” a senior law enforcement source said.

Hackett was charged with criminal possession of a weapon bomb, criminal possession of a defaced weapon, reckless endangerment and violation of a local law, police said.

He was awaiting arraignment in Brooklyn criminal court Thursday evening.