Two unrelated car accidents claimed the lives of a mother and her son early Sunday morning in West Allis, Wis.

Mary Moore, 45,  was struck by a car, while lying in the street at approximately 1 a.m. Sunday morning.

According to a report by the medical examiner, a witness behind the car that struck Moore initially thought the first car had gone over a speed bump.   But when the witness got closer,  they realized that a woman was lying in the roadway.

Moore was pronounced dead at the scene of the accident, authorities said. The driver who struck her was arrested a few hours later, according to police. The driver had left the scene.

ABC News affiliate WISN12 spoke to Wendy Muth, a neighbor, who called 911 after she heard a loud noise outside her house.

"I looked out and saw a body laying there," Muth told WISN12. "They were asking me, 'Are they breathing.' I said, 'They're not moving, so should I go out and see?' And you know-she-the person was gone already."

Approximately four hours after Moore was struck, her son, Thomas Olson, 22, was killed as he was being driven to the hospital.

Olson was riding as a passenger in his girlfriend's jeep, when the driver lost control of the vehicle, hit three parked cars and flipped over, according to a report by the medical examiner.  Olsen was ejected from the vehicle and later succumbed to his injuries at the hospital. His fellow passengers suffered non-life threatening injuries.

Police say alcohol may have been a factor in both of the fatal crashes. The person driving Olson to the hospital was arrested for a DUI after the accident.

West Allis Police Department Deputy Chief Charles Padgett told ABCNews.com that although Moore had been drinking, it was unclear how much alcohol she had consumed. The driver who allegedly struck her was also seen at a local tavern prior to the accident, but Padgett said police are not pursuing alcohol-related charges in that case at this time, he said.

The two fatal accidents happened within just two miles of each other under circumstances Padgett called "unusual and rare."

"I'm trying to think back, I've seen a lot of strange things," Padgett, a 24-year-veteran of the police force, told ABCNews.com. "I don't remember anything like this before."