ST. AUGUSTINE, Fla. -- Authorities say the theft of a charter jet that was reported stolen from St. Augustine and ended up more than 350 miles away near Atlanta was not part of a sinister plot, such as terrorism.

The 10-passenger plane, a $7 million Cessna Citation 7, was found at the Gwinnett County, Ga., Airport-Briscoe Field on Monday, said Darren Moloney, spokesman for the Gwinnett County Police Department. It remained there Tuesday, surrounded by orange cones.

"We've ruled out anything diabolical or sinister," Moloney said. "We didn't find anything threatening on the plane."

St. Johns County Sheriff David Shoar said his investigators have talked to witnesses and have an idea who stole the aircraft, but they don't know why.

"This is probably the first case of airplane theft that I've ever had to deal with," Shoar said.

The plane is owned by Pinnacle Air of Springdale, Ark., which had no comment but said they were cooperating with the investigation.

Crime scene investigators have gotten all the forensic evidence they need from the plane, and there was no evidence of weapons or drugs, Moloney said.

Bryan Cooper, assistant manager at St. Augustine Airport, said the plane was still there at midnight Saturday but was gone by 5 a.m. Cooper said there are three ways to get into the airport after midnight.

"You can fly in and land here, or have a key or authorized access or climb over the fence," Cooper said. "They could have used any one of the three."

The plane landed at Gwinnett sometime between 9 p.m. Saturday and 6 a.m. Sunday, Moloney said. It had some damage to the front edge of one wing but was not disabled, authorities said.

Although the plane landed when the airport's flight tower was not operating, officials said that is not unusual. Once on the ground, an automatic gate would have let the person out of the airport, Moloney said.

The Federal Aviation Administration is probing its own traffic system to see if there is any record of the plane flying during the time in question, FAA spokeswoman Kathleen Bergen said.

Channel 4's Jennifer Waugh reported that private aircraft are not required to file a flight plan, and a transmitter that would identify the plane to air traffic controllers was apparently not turned on.

Lisa Ray, spokeswoman at the Georgia Office of Homeland Security, had no comment on whether the theft raised larger questions of security at the airport, which is the fifth-busiest in Georgia. Two of the Sept. 11 hijackers, Mohamed Atta and Marwan al-Shehhi, trained there for a time.