James Brown of Sterling Heights, Mich., was being held without bail in the deaths of Demesha Hunt, 25, Renisha Landers, 24, Natasha Curtis, 29, and Vernithea McCrary, 28, The Detroit News reported.
A magistrate entered a not guilty plea on Brown's behalf and set his bond at $500,000 for each case. A preliminary hearing was set for May 17.
The bodies of Hunt and Landers were found in the trunk of an abandoned car Dec. 19, and those of Curtis and McCrary were found burned in a vehicle Dec. 25.
Brown is named on disinterment and arson counts. While not initially charged with murder, police said he is suspected of killing the women, three of whom were listed as escorts on a Web site.
The News said a second person named as a suspect in recent days was no longer in police custody. Police Chief Ralph Godbee said Brown was the main person involved in the slayings.
"He's a significant player in this whole scenario," said Godbee, who added he believes the murders happened outside of Detroit.