A truck driver found in a parking lot in Lincoln died of natural causes. That’s according to medical officials, who say an autopsy performed Friday indicates Tennessee trucker Brian Isdell died of a heart attack.But, police say the man was involved in some sort of altercation in the early morning hours before he died. The incident is still under investigation. A Lincoln police officer discovered the 55-year-old man on the ground in the parking lot around 3 a.m. Thursday.”We wanted to make sure that his death was not caused by a deliberate act. What will happen from this point, now that we know it was natural causes, is we will review the other circumstances in the case surrounding the altercation,” says Lincoln Police Chief Bill Flagg.Flagg says some sort of fight took place in this parking lot on Main Street with some local teens. “An argument ensued with the driver of the truck and a couple people in the parking lot,” Flagg says. While they know who is involved, he says they haven’t taken anyone into custody. Meanwhile, the incident is the talk of the town. “It’s kind of a hardship to think something bad might have happened to him,” says Alana Lloyd, of Lincoln.”We’re pretty soft-loving people around here. Everybody’s friendly. I just don’t understand,” says Rosemary Glidden, who was shopping in Lincoln Friday.While rumors are also circulating, Flagg asks for patience while they complete their investigation.”We have to get all the facts on the table, we have to collect all the evidence, we have to review that evidence. We don’t want to make a mistake. We need the time to do that,” he says.Flagg says at that point they will review what they have with the Penobscot County District Attorney’s office, to see what – if any – further action should be taken.