MARIETTA, Ga. (AP) — A 78-year-old man who had been reported missing was found dead inside his truck outside Atlanta, and his grandson and the suspect's girlfriend now face charges in connection with his killing, police said.

Edward Smith of Lilburn was reported missing Sunday after not being seen since Thursday, Cobb County Sgt. Dana Pierce said. Pierce tells that his body was found Tuesday night on a road in Mableton.

Pierce said Smith's grandson, 30-year-old Casey Ryan Collins, and 23-year-old Sarah Elizabeth Cook, both face charges of felony murder, The Atlanta Journal-Constitution reported (http://bit.ly/12XgQxK ). Arrest warrants obtained by the newspaper allege they stabbed and strangled Smith inside the older man's pickup truck, then drove around town in the vehicle with his body still inside.

The suspects, who are both from Mableton, were being held in the Cobb County Jail. Jail records do not list attorneys for them.

Police did not release information regarding a possible motive. An autopsy is pending to determine how Smith died, The Marietta Daily Journal reported.

Mableton is about 12 miles northwest of downtown Atlanta.