A neighbor called 911 after hearing gunfire, Clark said. When police arrived at the rowhouse, he said, the man had fled.
Blunt, whom police found in her bed, had gunshot wounds and was pronounced dead at the scene, Clark said.
Haynes did not show up for work Wednesday and "hasn't been seen," Clark said at a news conference at Police Headquarters.
"We need to talk to him," Clark said. He did not say where Haynes worked.
Clark said Haynes and Blunt had been dating for six months and living together for three.
He did not say whether the couple had a history of disputes, but said Haynes was "very well known to police" and was on probation.
Blunt's 6-year-old daughter and a 3-year-old boy she was watching, son of a friend, slept through the shooting, Clark said. They did not wake up until police arrived. Clark said the children were unharmed and with family members Wednesday.
Blunt's family could not be reached Wednesday. A neighbor said Blunt could often be seen in scrubs walking her daughter to school.
Clark said Haynes should be considered armed and "extremely dangerous." Anyone with information about Haynes' whereabouts is being asked to call the Homicide Unit at 215-686-3334 or 911.
Contact Maddie Hanna at 215-854-2771 or firstname.lastname@example.org.