Investigators believe the weapon was a high-powered rifle, Whitman said. The shot was fired at about 12:20 a.m., and the shooter may have been a New Year's reveler celebrating the New Year, police spokesman Sonny Jackson said.
Witnesses reported hearing several shots, and a second bullet was found in a snowbank in front of the home.
The victims were at a party with about 10 other people when the bullet pierced the front wall of the house, passed through the head of the woman, who was seated, and struck the girl in the side, Jackson said.
The woman died at the scene and the girl was pronounced dead at a hospital. It wasn't immediately known whether they were related.
No arrests had been made. Police offered a $2,000 reward for information.
Investigators believe the shot was fired from as far as 300 yards away, possibly from across a greenway flanking a walking path near the house, investigators said.
Police said they used lasers to trace the trajectory of the shot and to determine that one bullet killed both victims.
The house is in a neighborhood of modest single-family homes, duplexes and apartment buildings.
