Prosectors have concluded that Robert Rembert Jr., a truck driver from Cleveland, is a serial killer after he was indicted on multiple counts of aggravated murder in the slayings of four people.

On Tuesday, a Cuyahoga County grand jury indicted Rembert, 45, who has been in jail since Sept. 21 and held on a $1 million bond, according to Newsmax.

In 1997, Rembert was convicted of manslaughter for the murder of Dadren Lewis, 24, in a Cleveland parking lot, serving six years for the crime. However, Prosecutor Timothy J. McGinty said Rembert also killed three other people since his release, as well as another in 1997 before Lewis's death.

DNA evidence matched Rembert to the rape and strangulation deaths of Rena Mae Payne in May 1997 and Kimberly hall in June 2015, reported the Associated Press. He was also charged with fatally shooting Morgan Nietzel and his cousin, Jerry Rembert, in the head at a Cleveland home Sept. 20.

"Robert Rembert is a serial killer," McGinty said, according to USA Today. "So far, we know he's purposefully executed five people. An investigation of his activities as an over-the-road truck driver is currently under way."

Rembert has been indicted on a total of 25 charges: 10 counts of aggravated murder, six counts of kidnapping, four counts of rape, two counts of aggravated robbery and one count each of having weapons as a felon, grand theft and gross abuse of a corpse.