An Ormond Beach couple found dead over the weekend on the side of Interstate 4 had a history of drug abuse and investigators believe the man may have died of an overdose, Sheriff Mike Chitwood said Tuesday.

But that didn't put an end to the mystery as Chitwood said there was some concern with the woman's cause of death so investigators are awaiting the results of an autopsy.

How exactly Daniel Kelsey, 32, and Heather Kelsey, 30, wound up stopped along the highway and unresponsive outside of their car is unclear.

The couple's three children were found unharmed in their car seats inside of the maroon-colored Ford Freestyle by a trooper, Florida Highway Patrol spokeswoman Sgt. Kim Montes said.

The trooper found the car, its hazard lights blinking, on the right paved shoulder of eastbound I-4, northeast of State Road 44, about 1:30 a.m. Saturday, according to a sheriff's report.

The car hadn't been there more than 30 minutes because the trooper that found the seemingly disabled vehicle had been patrolling the area, Montes said.

Heather Kelsey was pronounced dead at 2:20 a.m. by a Volusia County Fire Services crew, according to the report. Daniel Kelsey was pronounced dead a couple of minutes after his wife of nearly six years.

Family members and friends expressed their shock and sadness on Kelsey's Facebook page.

Meghan Costello, who is married to Kelsey's brother Michael Kelsey, said she adored the bond the couple had and the love Daniel Kelsey showed his family.

"This year was hard for all of us, but the love you showed for Mike, Heather, your mom and those boys never faded," Costello wrote.

"Not the news I wanted right now. Another family member gone," Brock Beckman wrote. "Rest easy cousin. Watch over all of us."

Chitwood said there were no signs of foul play in the couple's deaths. There were also no outward signs of trauma.

"At first glance, investigators feel he was an overdose," Chitwood said. "There was some concern with the female that an autopsy will clear up."

Chitwood revealed the latest details on the couple's death at a press conference shortly after he was sworn in on Tuesday as the 27th sheriff of Volusia County at the Bethune-Cookman University Performing Arts Center in Daytona Beach.

"Because of their problems, they were in Quincy, Florida, and were making their way back," Chitwood said.

The couple's three sons — Aiden Kelsey, 2; Nicholas Kelsey, 1; and infant Joseph Kelsey — were being cared for by relatives of Daniel Kelsey, Chitwood said.

John Harrell, spokesman for the state Department of Children and Families, said the agency is working with local authorities.

"We're very sensitive to what these children have been through. That's the main priority," Harrell said.