The man, Joaquin Soto Marroquin apparently suffers from mental problems. The police found his sister's body in an advanced state of decomposition in a bed. The body was taken to the coroner's office in Tulancingo.
The elderly man told police his sister, Clementina, was sick and not dead, the El Sol de Hidalgo newspaper reported.
Tests reveal that the woman died about eight months ago from natural causes. Neighbours had noticed that Soto Marroquin's sister was not around, but they never suspected she had died, El Sol said.