The parents of a 2-year-old Idaho boy who disappeared in July have been named suspects in the case, authorities said Monday.

Lemhi County Sheriff Lynn Bowerman said Jessica Mitchell and DeOrr Kunz Sr. have been "less than truthful" in the disappearance of their son, who was last seen at a campsite near the Timber Creek Reservoir in Leodore where he was staying with his parents, great-grandfather and another adult.

Bowerman said that he believes the parents know the location of DeOrr Kunz Jr., of Idaho Falls, and whether he's dead or alive.

He said the couple has not been arrested and no warrants have been issued. Bowerman said an arrest isn't imminent because the situation could change if DeOrr Kunz Jr. is found.

Bowerman and his deputies have scoured the rugged terrain surrounding the remote Idaho campsite for the boy -- using sonar imaging equipment to probe a nearby reservoir and searching a wolf den for any trace of the child.

At 2:30 p.m. on July 10, the child's 25-year-old mother called 911 from the campsite to report her son missing. She and the boy's father said they left their son with his great-grandfather while they went off to explore. The great-grandfather believed the boy was with his parents, according to police.

What happened during the 20 to 45 minutes the child was alone is a mystery to authorities.

The family's campsite sat approximately 40 yards from a fast-moving creek -- 4 to 6 feet in width and about a foot deep -- that spills into the Timber Creek Reservoir, a half mile from where the toddler was last seen.

The boy's parents have said they believe their child was abducted.

Bowerman, however, told FoxNews.com in July that he's not convinced of an abduction, noting that no other campers were seen or heard in the area at the time of the disappearance.

He also described the terrain as "steep and rugged" and said vehicles can reach the site but "the road is extremely rough."

"We don't have any evidence that somebody kidnapped this child," Bowerman said.

FoxNews.com's Cristina Corbin and The Associated Press contributed to this report.