A 78-year-old man reported missing was found dead inside his truck Tuesday night, Cobb County police said. And the man’s grandson and girlfriend have been charged with killing the older man.

Edward Smith, of Lilburn, was reported missing Sunday after not being seen since Thursday, Sgt. Dana Pierce with Cobb police said.

Tuesday night, Smith was found dead inside his truck on Kemolay Road in Mableton, Pierce said. An autopsy will be conducted to determine the cause of death, but it is being treated as a homicide, according to police.

Smith’s grandson, Casey Ryan Collins, 30, and Collins’ girlfriend, Sarah Elizabeth Cook, 23, both of Mableton, were arrested and charged with felony murder, Pierce said. Both were booked into the Cobb County jail, where they were being held late Tuesday without bond.

Police did not release information regarding a possible motive.