DETROIT, MI — Police in Detroit believe a killer may be targeting women who advertise adult escort services on backpage.com. Two dead women were found in the trunk of a burning car on Christmas morning, less than a week after the bodies of another two women were found in a car abandoned on the city’s east side.

The Detroit Free Press reports. No cause of death has been determined for the four women, all of whom were in their 20s.

Three of the four women had profiles in the adult section of backpage.com, a classified ad site similar to Craigslist.

Police say the link is “disconcerting,” but they stopped short of saying they believe the deaths are the work of a serial killer.

“We are not passing judgment on any individual who is utilizing this website, yet we felt it was imperative to alert the public that deciding to meet unknown persons via the Internet can be extremely dangerous,” Detroit’s chief of police told reporters.