Er sollte tot...

Pensioner Johannes Obermaier was beaten to death in his home. The suspect is Maria Lorenz, who had been looking after the lonely old man in recent months and had been appointed by him as his sole heir. However, Maria seems to have an alibi. It gradually emerges that Maria worked as a prostitute, married a property owner who died 15 days after the wedding and took a lot of money from lonely men by telling lies. What does she have to do with the murder?