PUTNAM COUNTY, Fla. -- Authorities believe a 15-year-old girl at the center of an amber alert issued Thursday night may be riding in the truck of a homicide victim.

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DETAILS: FDLE Info On Amber Alert

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Investigators believe 15-year-old Morgan Leppert, from Putnam County, may be with her boyfriend, 22-year-old Toby Lowry. They were seen riding in a Toyota Tacoma registered to James Thomas Stewart.

Investigators said 66-year-old Stewart's body was found at his Cherry Laurel Drive home in Melrose Thursday morning, about 20 miles east of Gainesville. Stewart was found by Putnam County sheriff's deputies who responded to a call from persons concerned because they had not heard from him in several days.

The Putnam County Sheriff's Office said they then discovered Stewart's telephone number was found on a cell phone belonging to Leppert. Leppert had been reported missing to the Putnam County Sheriff's Office on April 22, 2008 by her mother. At that time she was believed to be in the company Lowry.

Investigators said they learned that Stewart's vehicle, a silver in color 2003 Toyota Tacoma, extended-cab, long-wheel base, two-wheel drive pickup truck, was missing. The vehicle's Florida tag, 193KLR, was entered into the Florida and National crime information system, which caused the sheriff's office to receive several "hits" where the tag had been run by various law enforcement agencies prior to it being entered. Those responses came from several locations along Interstate 10, with the last response occurring at approximately 12:30 am on the morning of the 1st of May from Katy, Texas, investigators said.

Warrants have been issued for Lowry, charging him with Grand Theft of the vehicle and Interference with Custody of a Child. Officials also call him "a person of interest in Stewart's death."

An Amber Alert has been issued, nationwide, for Leppert.