A 13-year-old boy found dead in grass had been shot and stabbed multiple times, the DeKalb County Medical Examiner said Thursday.

The body of Marquis Overstreet was found around 9:15 a.m. Wednesday by a landscaper in the 5300 block of Biffle Downs Road, off Panola Road near Stone Mountain, Mekka Parish, spokeswoman for DeKalb County police, told the AJC.

Overstreet sustained a gunshot wound and had been stabbed multiple times, according to Pat Bailey with the medical examiner's office.

Investigators believe the teen may have been shot in the vicinity and tried to get help, but instead collapsed and died, Parish said. Police believe Overstreet was killed between Monday morning and Tuesday, she said.

Overstreet's mother told the AJC that her son ran away from home about two weeks ago, but apparently had been staying with friends. Keisha Langhorne, who reported Marquis as a runaway to police, said she believes her son was on the way to his girlfriend's house for a Fourth of July cookout, but never made it.

"I don't have a clue what happened," Langhorne said Thursday night.

Langhorne said the mother of her son's girlfriend called Tuesday to tell her detectives had been showing a picture of Marquis to people in the neighborhood to help identify the boy. Langhorne called the medical examiner's office and then police headquarters, where she positively identified her son based on a cell phone picture.

"I glanced at it briefly," Langhorne said. "I didn't really want to see."

Now, Langhorne said she's hoping someone will come forward with information about what happened to her son. So far, investigators have not named any suspects in the case.

Funeral arrangements for Overstreet have not yet been completed.