Denver ? A single bullet ripped through the wall of a house early Tuesday morning, killing an 11-year-old girl and a woman attending a New Year’s party inside, investigators said.

A 25-year-old man was later arrested at his home on investigation of two counts of first-degree murder, police spokesman Sonny Jackson said.

Investigators believe the weapon was a high-powered rifle, Police Chief Gerry Whitman said. The shot was fired at about 12:20 a.m., 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. Their identities were not released Tuesday night.

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.