By Emily Le Coz

TUPELO, Miss (Reuters) - A person posing as a police officer may be responsible for a pair of Mississippi highway murders, according to authorities searching for the killer.

Thomas Schlender, 74, was found dead in his pickup truck on an interstate median on May 8, and three days later Lori Anne Carswell, 48, was found dead in her Pontiac Grand Am on a highway shoulder.

Both had been shot in sparsely populated areas of northern Mississippi, said Mississippi Bureau of Investigation spokesman Warren Strain, who declined to say what type of gun was used.

There were no witnesses, officials said.

"There's only two people that could give us any information on what's happened and, it's sad to say, but they can't answer any questions at this time," said DeSoto County Sheriff Bill Rasco, who is assisting in the investigation.

Carswell, of Hernando, Mississippi, was driving home from Tunica, Mississippi, where she'd just clocked out from her job at a casino, said Tunica County spokesman Larry Liddell.

He said Schlender, of Raymond, Nebraska was passing through Mississippi on his way to pick up his grandson in Florida.

Both shootings happened in the early morning hours, Liddell said.

"There are some similarities between the two incidents, mainly the fact that they happened alongside a Mississippi highway," Mississippi Bureau of Investigation Director Lt. Col. Larry Waggoner said in a statement.

"The concern is that someone is posing as a law enforcement officer and that's how these vehicles end up on the side of the road."

The bureau urged motorists to call 911 or *47 if they're being pulled over and it's unclear whether a legitimate police officer is making the stop.

It's also possible the killer could be posing as a someone with car trouble, Strain said.

"This is stuff you see off of TV. It's not something you see in Mississippi, anywhere in Mississippi I've ever heard of," said Panola County Coroner Gracie Gulledge, who pronounced Schlender dead at the scene.

(Editing by Corrie MacLaggan)