Anthony Sowell case leads investigators to another alleged Cleveland serial killer, Joseph Hartwell

(CBS/AP) CLEVELAND, Ohio - When a cold case unit began a special investigation of the 11 bodies that were unearthed at the home of Anthony Sowell on the east side of Cleveland in 2009, they discovered DNA that led them to another serial murderer in the area.

Joseph Harwell, 50, was indicted Tuesday on charges of raping and killing 27-year-old Mary Thomas in 1989, and 33-year-old Tondilear Harge in 1996, based on the cold case unit's investigation, officials say.

The investigators looked at 75 unsolved slayings of women within a three-mile radius of the two homes where Sowell had lived since the 1980s - the "surge" area, they called it.

The cold case unit, which includes retired homicide detectives and scientists at the coroner's office, pored over case files to see if evidence from the original crime scenes had been preserved and could be tested for DNA.

In November 2010, they got a hit. Harwell's DNA was traced to Thomas, who was found in an abandoned building in the area near Sowell's home March 28, 1989. The coroner ruled that she had been strangled with a red cord and beaten to death. Thomas was three months pregnant when she died.

Investigators had already been looking into Harwell since 2008, when his DNA was matched to the Harge killing. Her case was not part of the surge investigation, but her body was also found in an empty lot near Sowell's home.

Harge's death was ruled a " homicide undetermined."

Now, 46 of the original surge cases remain active. Most of them are on hold, waiting further testing at the coroner's office. So far, Thomas is the only victim to produce a DNA hit.

Harwell is incarcerated at Richland Correctional Institution in Mansfield, an hour south of Cleveland, serving 15 years to life after pleading guilty to killing Teresa Vinson in Columbus in 1997. He is eligible for parole in 2012.

Harwell has a long criminal history dating back to the 1970s, including a conviction for felonious assault in 1989, when he attempted to strangle a woman who survived.

Click here for complete coverage of the Anthony Sowell case on Crimesider