M is the murderer

A serial killer (played by Peter Lorre) who committed crimes against little girls appears, and people in the city are panicked. The police were out in force and conducted frequent surprise inspections. The gang leader (Gustaf Gründgens) has his business severely affected and decides to use the beggars' anonymity to lay a dragnet. The blind beggar selling balloons (played by Georg John) identifies the killer through the whistle of "In the Palace of the Demon King", and his accomplice (played by Carl Balhaus) takes the opportunity to mark the initial "M" of "Mörder" on his back. Although the police locked the killer's residence, the killer was besieged by beggars in a commercial building and became a turtle in the urn. Late at night, in a private court set up by the gang, how will the killer defend himself?