Detroit police said two women were found dead Dec. 19 on the city's east side.
The bodies were found in a newer-model Chrysler 300 parked between abandoned houses on Promenade Avenue near Chalmers Street.
Victims' family members said 23-year-old Renesha Landers and her 24-year-old cousin Denesha Hunt went to a party Saturday night at Blackberry on Grand River Avenue. The family reported them missing when they did not return home that night.
Landers, who works at a Chrysler plant, had recently purchased the car.
Detroit homicide said investigators were on the case.
The Wayne County Medical Examiner's Office said the cause of death were pending toxicology reports. After initial autopsies, there were no signs of external trauma, the medical examiner said.