(CNN) -- A search has been launched for a 50-year-old sex offender suspected in the killings of six people whose bodies were found in and around a house in Cleveland, Ohio, police said Friday.

The incident began unfolding a month ago, when a woman accused Anthony Sowell of rape and felonious assault, Cleveland Police spokesman Lt. Thomas Stacho told CNN.

"Once we were able to get the cooperation of the victim, we secured an arrest warrant for Mr. Sowell and subsequently a search warrant for his premises," Stacho said.

On Thursday, detectives from the department's sex-crimes unit and members of its SWAT team went to Sowell's home to execute the warrant and to arrest the suspect, but he was nowhere to be found, Stacho said.

What they did find were the badly decomposed remains of two bodies on the third floor of the house, which is owned by an elderly relative of Sowell who did not live there, Stacho said.

A subsequent search on Thursday revealed what appeared to be a freshly dug grave under the stairs in the basement, he said.

On Friday, investigators returned to the house, dug up the grave and found a third body, he said.

A further search of the house and property found two more bodies in a crawl space and a sixth body was found in a shallow grave outside the home, Stacho said.

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None of the bodies has been identified, and the genders of only two -- those found on the third floor -- have been determined, he said. Both were female.

"He apparently is a serial rapist," Stacho said about Sowell, who he said makes his living as a "scrapper."

"He walks around and picks up scrap metal and takes it to junk yards to make a few pennies."

Sowell pleaded guilty to attempted rape in a 1989 case for which he was imprisoned from 1990 to 2005, Stacho said.

Authorities plan to continue their search of the house on Saturday.

