Stanton, Calif. ? A kidnapped 5-year-old girl was sexually assaulted and suffocated before her nude body was dumped near a rural road in what investigators said Wednesday was a “calling card” from the killer warning that he intends to strike again.

Orange County Sheriff Mike Carona said Samantha Runnion was asphyxiated sometime Tuesday, though he didn’t say how she was killed.

Jude Labastida, 8, a neighbor who used to play with Samantha Runnion, pauses at a table filled with flowers, toys and cards in front of Samantha's home in Stanton, Calif. Samantha, 5, was abducted and killed this week.

Autopsy results showed she was alive for hours after her abduction Monday evening. The sheriff also said Samantha may have fought against her killer and inflicted “injuries to his hands, arms and possibly face.”

“Don’t sleep, don’t eat, because we’re coming after you,” Carona warned the killer in a televised news conference near the girl’s home in Stanton.

Samantha’s body was found Tuesday afternoon, less than 24 hours and about 50 miles from where she was abducted outside her apartment building. She was nabbed by a man who pulled up in a light green Honda or Acura car and asked for help finding his puppy. Samantha was playing with a 5-year-old friend at the time.

Authorities said there was no prime suspect, and Carona warned parents in the area to tell their children to stay away from strangers.

“We believe that he is a serial rapist and perhaps a serial killer and would strike again,” the sheriff said.

Based on the playmate’s account, police described the abductor as a Hispanic man with slicked-back black hair and a thin, black mustache. FBI agent Richard Garcia said the girl was able to identify speech patterns, leading investigators to believe the man is American rather than foreign.

The abduction was at least the third high-profile disappearance of a child in the United States this year. Seven-year-old Danielle van Dam of San Diego was found dead, and a neighbor is on trial. Fourteen-year-old Elizabeth Smart of Salt Lake City has been missing since June 5.