Mississippi authorities are questioning a man suspected of impersonating a police officer to determine whether he is involved in the killings of two motorists on state highways, a sheriff's investigator said Thursday.

The man was picked up after stopping two drivers, Humphreys County Sheriff Investigator Sam Dobbins told CNN. He was driving a blue Mercury Marquis that used to be a police car and still had flashing blue lights on top, Dobbins said.

Investigators had raised the possibility that someone posing as a police officer is to blame for the shootings, which happened this month about 55 miles apart.

In the first incident, Tom Schlender, 74, was found dead in his car about 1:30 a.m. in the median of an interstate highway last week. A few days later, Lori Anne Carswell, 48, was found dead outside her car on the shoulder of a state highway.

Because of the places where the drivers were found, and because nothing was found wrong with their cars, authorities say it's possible someone posing as a police officer may have signaled to the drivers to pull over.

Authorities say the victims did not know each other.