After nearly 35 years, police have identified the man they say raped and murdered 18-year-old Traci Hammerberg.

Hammerberg, of Saukville, was found partially naked in a Town of Grafton driveway at 5:45 a.m. Dec 15, 1984.

Through the use of DNA evidence and forensic genealogy, police said Tuesday, they determined that Hammerberg was raped, strangled and bludgeoned to death by then-21-year-old Philip Cross, who died of a drug overdose in 2012.

On the night of her murder, Ozaukee County Sheriff James Johnson said, Hammerberg left a Saukville house where she was babysitting, walked to a Saukville grocery store and then met up with friends. They drove her to Quade’s Tavern in Port Washington, where she told the bartender she was going to a party in Grafton.

The friends went to a party in Port Washington, where they played a beer drinking game and smoked marijuana. She is believed to have left the party on foot around 12:30 a.m. It would have been a 3.7-mile walk along State Highway 33, but Johnson said it was not uncommon for Hammerberg to make the walk home from Port Washington to Saukville.

Hammerberg was not seen again until 5:45 a.m., when a man found her battered body lying on his Maple Road driveway. Blood was found on the snow and in the trees around her.

At the same time, two different hunters in the area saw a car speed away from Maple Road with its headlights off.

Semen found at the scene was used to develop a DNA profile. Blood found underneath her fingernails matched that DNA profile.

"Without a doubt, the DNA recovered from Traci's body was from the person that raped and killed Traci Hammerberg," Johnson said.

Extensive investigation

The Ozaukee County Sheriff's Office has been investigating the case for the past 34 years. Since 1984, the agency has received assistance from the state Department of Justice Division of Criminal Investigation. The FBI Behavioral Analysis Unit also provided a criminal profile.

Hundreds of witnesses were interviewed, and more than 400 men were eliminated from the pool of suspects through blood type and DNA analysis.

In March 2019, investigators decided to focus on forensic genealogy, and sought out assistance from the Los Angeles FBI Forensic Genetic Genealogy Team, which helped identify Joseph James DeAngelo as the Golden State Killer.

Investigators sent DNA evidence to a private lab, which developed a DNA profile. The profile was uploaded to a genetic genealogy database, which was used to identify family members of the suspect. The closest relative was a second cousin.

For the next step, investigators needed to build an extensive family tree tracing back four generations. Then, they identified any male second cousin that would have been between the ages of 16 and 60 in 1984.

This process led police to identify Cross as a potential suspect Aug. 28. When Cross died of a drug overdose in 2012, the Milwaukee County Medical Examiner's Office obtained a DNA card.

Several days later, the State Crime Lab in Madison determined Cross' DNA profile matched the semen swab and fingernail clippings obtained during Hammerberg's autopsy.

Cross was not a name known to Johnson or any of the other investigators working the Hammerberg case.

Connecting the dots

As they dug into Cross' background, they learned the 21-year-old had worked second shift, from 4 p.m. to midnight, at Rexnord Plastics in Grafton. Police believe he could have picked up Hammerberg on Highway 33 as he drove home to his parents' house on Green Bay Road in the Town of Grafton.

Hammerberg was familiar with the driveway where she was found, and Johnson said she may have directed Cross to that driveway if they were looking for a place to hang out. Cross had a volatile temper, Johnson said, and he may have acted violently if Hammerberg denied his sexual advances.

Witnesses reported that Cross smoked Marlboro cigarettes, which were recovered next to Hammerberg's body. Hammerberg smoked menthol cigarettes.

Cross' checkered past

As police investigated Cross' background, many people described him as a drug and alcohol abuser who was ill-tempered, abusive and quick to fly off the handle, Johnson said.

Cross had a history of police interactions. He briefly attended Port Washington High School in 1978, until he was sent to Ethan Allen School for calling in a school bomb threat and stealing a car, Johnson said.

Cross was released from the correctional school in 1981, and the next year, he was jailed on drug charges in Ozaukee County. The year after that, he punched a hole in the wall of a Port Washington hotel following an argument with his girlfriend.

He was convicted of forgery in 1983 and spent more than a year in state prison.

Five months after he was released from prison, Cross started working at Rexnord Plastics, where he received complaints for leaving a vulgar note for coworkers, using bad language and causing damage to a machine.

In 1991, Cross was accused of strangling a woman with his belt while she was giving him a ride home from a Sheboygan tavern. Cross admitted to police that he was involved, but he provided a different account of the incident.

Between 1992 and 2004, police responded to Cross' Sheboygan house on at least 15 occasions for domestic abuse, throwing objects and drug and alcohol abuse.

In 2012, an arrest warrant was issued for Cross after he threatened a hospital employee who told him he would not be able to see his girlfriend.

Forensic genetic genealogy is a hot topic in forensic science, said Jennifer Naugle, deputy administrator of the State Crime Lab. She said the State Crime Lab has been learning about forensic genetic genealogy in the past year, but this type of testing does not yet occur in Wisconsin.

“This has become a great opportunity for Wisconsin law enforcement agencies to reach out to places like L.A., to be able to use it as an investigative lead … and then we are able to finish up the end of the story,” Naugle said.

Johnson said the case would never have been solved without assistance from the DOJ’s Department of Criminal Investigation, the State Crime Lab and the Los Angeles FBI Forensic Genetic Genealogy Team.

“While many of us may not have known Traci, we wanted justice for her and her family,” he said. “We became her voice when she could no longer speak.”

Contact Jeff Rumage at (262) 446-6616 or jeff.rumage@jrn.com. Follow him on Twitter at @JeffRumage or Facebook at www.facebook.com/northshorenow.