(CNN) -- A man who police say may have been killed by someone posing as a police officer was missing his wallet when he was found, a family member said Wednesday.
Tom Schlender, 74, was found dead last week in his car about 1:30 a.m. in the median of an interstate highway.
A few days later, another driver, 48-year-old Lori Anne Carswell, was found dead outside her car on the shoulder of a state highway.
The shootings took place about 55 miles apart, and the victims did not know each other, authorities said.
According to bank records the family has looked up, Schlender withdrew around $600 for the trip before he left Nebraska, Schlender's son-in-law Matthew Anderson said.
Schlender's wallet was missing at the crime scene, Anderson said. The family would not indicate whether there has been any activity on Schlender's accounts since the killing.
Carswell's family declined to comment.
Because of the places where both 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.
The Mississippi Bureau of Investigation is asking for the public's help to find the person.
The agency was receiving leads and processing forensic evidence, bureau spokesman Warren Strain said.
John Champion, district attorney for the state's 17th District, said both shootings occurred in "very remote areas."
Authorities called on people to be careful if they are pulled over and feel uneasy.
They advise drivers to call 911 and verify that a legitimate officer is pulling them over, or drive to a well-lit, crowded place before stopping, actions permitted under Mississippi state law.
Anderson, who lives in Ashland, Nebraska, said the family is in a state of shock.
Schlender was headed to Pensacola, Florida, to pick up one of his grandsons from college and bring him back to Nebraska for the summer.
Schlender's daughter, Tracy Anderson, called her father around 6:30 that evening, while he was on the road. He was between St. Louis, Missouri, and Memphis, Tennessee, at the time. They had a nice conversation, and nothing indicated any problems, Matthew Anderson said.
CNN's Tristan Smith contributed to this report.