A police spokesman on Thursday confirmed the 48-year-old officer shot himself near a lake in the city's Kaulsdorf district. He reportedly had personal problems.
"There's no evidence of foul play," said the spokesman.
The officer, who worked for the police securing the German parliament building, beat a female postal office worker in a restricted area of a Bundestag building in Berlin on Wednesday night in what may have been a robbery attempt.
The woman suffered a blow to the head and was taken to hospital.
The Deutsche Post office stands in the Marie Elisabeth Lüders building, which houses MPs' offices and conference rooms. It is in an area restricted to authorized people such as MPs and Bundestag employees.
The attack comes after intense discussion in recent months over security of the Bundestag buildings and the Reichstag, which was reportedly a possible target of a Mumbai-style armed siege by Islamic extremists.