Clarksville, Tenn. ? The daughter of late country music singer June Carter Cash was found dead in a parked bus along with a Nashville bluegrass fiddle player, authorities said.

Officials said Saturday that carbon monoxide from six propane or kerosene heaters on the bus may have killed the two and that an autopsy was planned. The bodies were found Friday afternoon.

Ted Denny, spokesman for the Montgomery County Sheriff’s Department, said Saturday that the deaths were “suspicious.” He said emergency medical workers found drug paraphernalia, including needles and pipes, on the bus near the bodies.

Investigators identified the victims as Rosey Nix Adams, who was the 45-year-old stepdaughter of late singing legend Johnny Cash, and Jimmy Campbell, 40, a bluegrass fiddle player who performed and recorded in Nashville for more than a decade.

Adams and her husband, Philip Adams, had recently sold a home in Montgomery County and were preparing to travel in the bus. They had parked the bus behind the house for repairs.

Investigators said the bus may have been owned by the late bluegrass pioneer Bill Monroe. Emergency workers found memorabilia from Monroe and Johnny Cash on the bus, such as autographed pictures.

Rosey Nix Adams, also known as Rosey Carter Adams, was the daughter of June Carter Cash and her second husband, Richard “Rip” Nix. She was a songwriter and had pursued a performing career.

Campbell was a member of The Sidemen, a band of Nashville session players, and had toured and recorded as leader of his own band.

“The Cash and Carter families are shocked and deeply saddened by the untimely death of Rosey Carter Adams,” family spokesman Kirt Webster said in a statement.

“The family has suffered greatly this year by the successive passing of Rosey’s mother, June Carter Cash, and her stepfather, Johnny Cash, in just over five months.”

Rosey Nix Adams’ mother died in May, and Johnny Cash died last month.