The 39-year-old was arrested in connection with the death of an 88-year-old woman at Emblehope House sheltered accommodation on Allendale Road, Farringdon, Sunderland, on Friday.
The 88-year-old, who has not been named, was treated by paramedics but later died.
A Northumbria Police spokeswoman said: "A 39-year-old woman who was arrested on suspicion of murder was released on bail.
"Inquiries are ongoing and police continue to appeal for witnesses to come forward."
Northumbria Police officers increased patrols in the area.
Temporary Chief Supt Kay Blyth said: "People will understandably be concerned by this incident, especially the elderly.
"We will have extra officers on patrol in the area to answer any questions they may have and reassure them."
She said the dead woman would not be named until her family had been informed.