Boston Police say Yvonne Lewis shot a relative in the head around 12:40 p.m., then was arrested about five hours later in Peabody.
Clive Francis, 49, of Mattapan, was taken to Brigham and Women's Hospital, where he was pronounced dead, police say.
The Globe reports Lewis is a former Boston Police employee.
Police had issued a BOLO - including notices on Twitter - that Lewis had fled in either a red Nissan with Massachusetts plates or a white Lexus with George plates, and that in either case, she was to be considered armed and dangerous.
She is scheduled for arraignment on Monday in West Roxbury Municipal Court.
The victim is Boston's third murder victim in the past three days.