A grand jury on Tuesday returned an indictment on two counts of first-degree murder against a 27-year-old Upper Marlboro man whom police have called a serial killer who is suspected in at least three other slayings.

Jason Thomas Scott was indicted in the deaths of Delores Dewitt, 42, and her 20-year-old daughter, Ebony, Prince George’s County State’s Attorney Glenn Ivey said. Their charred bodies were found March 16, 2009, in a burning car in Largo. That was just two months after another mother and daughter, 45-year-old Karen Lofton and 16-year-old Karissa, were found shot to death in their Largo home.

Scott is also suspected in the 2008 death of a Bowie woman who was shot and whose home was set on fire.

Ivey said Tuesday there was an “ongoing investigation” into Scott by Prince George’s County Police’s homicide unit. Chief Roberto Hylton said his investigators were working with other law enforcement agencies to determine whether Scott is connected to any other homicides.

Scott has been in custody since September when federal authorities arrested him on charges that he was selling firearms from the parking lot of his job at UPS. Scott has since had charges added that include carjacking and child pornography.

Last week, Hylton called him a serial killer and predicted Scott would go down as one of the “most notorious criminals in America.”