Simone Robinson, 37, of Wilmington died on Monday afternoon. She had been hospitalized since she was assaulted shortly before 8:00 p.m. Sunday.
That night, officers responded to the area of 25th and Thatcher Street regarding an assault.
On the scene, they found Robinson unresponsive, lying on the sidewalk with severe injuries to her head.
Witnesses identified the suspect as her ex-boyfriend, 31-year-old Gregory Griffin, of Bear.
Police say Robinson's children were present for at least part of the assault.
Griffin was later arrested at a relative's home in Elkton, Maryland.
Charges against Griffin were upgraded to murder.
He was being held behind bars without bail.