Authorities said the bodies had not been found, but prosecutor James Powell said the evidence showed that the family was dead. A funeral home van left the search area early in the afternoon, but officials would not say what the vehicle was transporting.
In a Yazoo County courthouse about 100 miles away, Earnest Lee Hargon heard the capital murder charges read and was ordered held without bond.
He is a cousin of Michael Hargon, who disappeared on Feb. 14 along with his wife Rebecca and their 4-year-old son, James Patrick. Friends and family of the missing family, many visibly shaken, watched the brief court appearance.
Powell said the slayings occurred during the kidnapping of one or more of Michael Hargon's family. Asked about a possible motive, Powell said, "I don't have to show a motive" to prosecute Hargon for capital murder. He said Hargon had acted alone.
Authorities this weekend spent two days searching near Earnest Hargon's 160-acre Smith County property about 100 miles from Michael Hargon's home, using helicopters, dogs, horses, and manpower, reports CBS News Correspondent Cynthia Bowers.
The suspect was arrested at his home on Friday on unrelated drug charges. Minutes before lawmen were to bring the truck driver into the courtroom Monday morning, Mississippi Highway Patrol spokesman Warren Strain announced the delay due to "profound new developments" in the county where the search is being conducted.
State troopers and deputies closed entrances to the land while helicopters and state Crime Lab trucks moved in to assist in the ground search. The property consists mostly of pine woods.
Intense searches of Hargon's home and 160 acres around it were carried out over the weekend by teams using horses, off-road vehicles, a helicopter and tracking dogs.
Blood and spent bullet casings were discovered at the family's home in Yazoo County after the three disappeared. Investigators have not found a .22-caliber weapon that apparently was fired in the home.
Investigators also have been checking a piece of land that Michael Hargon recently inherited from his uncle, Charles Hargon, to determine if it is linked to the disappearance, said Jennifer Hargon, Michael's sister.
Earnest Hargon, Charles Hargon's adopted son, was not included in the will, she said. Strain said the property is a consideration in the case, but not necessarily a motive.
"It could be a potential motive, but it's not the only one," Strain said.
Families in the area said the land being searched was owned by Tony Moran, whose family lives about a mile from the property. Family members at the Moran home would not comment on the search. The Moran property is several miles away from Earnest Hargon's home near Taylorsville.