HOUSTON -

A shooting at a northeast Houston house left one woman dead and two men injured Wednesday.

Houston police said the shooting happened at a home in the 1100 block of Neyland shortly before 5:30 a.m.

Investigators said a woman, identified by relatives as 57-year-old Frankie Cooper, was found shot to death in her bed. Her 21-year-old son was injured.

A family friend who suffered critical injuries called 911.

"She had open-heart surgery and could barely walk, never went out," said Barbara Waldrup, Cooper's sister.

Police said when they showed up to the house, the son answered the door covered in blood and holding a knife. Officers found the other man on the couch and the woman in her bedroom.

"They were unsure at that point what the call was concerning. They arrived to find three individuals inside -- one that was a female ultimately pronounced deceased at the scene and two males that were transported to the hospital with injuries," said Mark Coleman with HPD Homicide.

One officer told KPRC Local 2 that he believes a pellet gun was used to kill the woman.

Cooper leaves behind five children.

A motive for the shooting is not yet known. Investigators said Cooper's purse was missing, but her wallet was not.