(CNN) -- Milwaukee, Wisconsin, police have arrested a man whose DNA linked him to the bodies of nine women killed over 21 years, officials said at a news conference Monday night.



Walter E. Ellis, 49, was arrested after police matched a DNA swab taken from him last week to the victims.



Walter E. Ellis, 49, was arrested after police matched a DNA swab taken from him last week to DNA left on the bodies of nine women killed since 1986.



Police said eight of the women were prostitutes and one was a runaway involved with drugs. They were all killed within a 3-square-mile area of Milwaukee's north side.



"This case was solved with shoe leather and science," Milwaukee Police Chief Edward A. Flynn said. "Continuing advances in DNA technology have enabled us to link these homicide cases, and it was good police work pursuing numerous leads that led to the arrest of a suspect."



The homicides occurred between 1986 and 2007, police said.  See where the bodies were found »



Ellis was charged Monday with two counts of first degree murder relating to two of the deaths: 41-year-old Joyce Mims, who was killed in 1997, and 28-year-old Ouithreaun Stokes, who was killed in April 2007. Police said more charges are likely.



It wasn't immediately clear whether Ellis had obtained an attorney.



Police said other victims linked to Ellis through DNA were: Tanya L. Miller, killed in 1986; Deborah L. Harris, killed in 1986; Sheila Farrior, strangled in 1995; Florence McCormick, strangled in 1995; Irene Smith, killed in 1992; Carron D. Kilpatrick, killed in 1992, and Jessica Payne, killed in 1995.



Flynn told CNN it was hard for investigators to discern a geographic pattern for the homicides. In the 20-year period, more than 2,000 slayings occurred in Milwaukee, he said -- 200 of them in the same area where the bodies were found.



Another challenge investigators faced was the developing technology of DNA evidence. The technology in 2009 far exceeds that available in 1986 or even 2002, he said. It was only this year that police were able to link the nine homicides with the same DNA pattern.



Even then "we did not have anyone to match our DNA profile against, until we were able to get [Ellis'] toothbrush," he told CNN. A Wisconsin law passed in 2000 mandated the DNA collection from convicted felons. Ellis was released from prison in 2001 without having his DNA sample collected, Flynn said.



Because his name had surfaced in the investigation and because he was also listed in two FBI databases, authorities decided to investigate him further and were able to obtain the search warrant that allowed them to collect his DNA from his toothbrush, the police chief said.



News of Ellis' arrest shocked those who knew him.



"That was just my ex-boyfriend," his former girlfriend, Chanita, told CNN affiliate WISN-TV. She asked that her last name not be used. "I didn't know nothing about nothing like this. I'm getting shivery now cause you're talking about some strangling stuff. Lord have mercy on me. I'm just a wreck right now. I can't believe this. I'm trembling in here. I'm shakin'."



Chanita said she dated Ellis for four years.



"I can't believe it. This is a shock," she told WISN. "I got like goose bumps on my arms instantly when you told me that. I'm like no way -- not Walter -- I can't see him hurting nobody."



For relatives of the victims, the news brought mixed emotions.



"I knew they was gonna get him, I knew it," Patricia Donald, best friend of victim Deborah Harris, told WISN. "Finally he can't hurt nobody anymore."



For her and others, like Sandy Farrior, whose daughter Sheila was linked to Ellis, it was news that helped bring closure.



"Late justice is better than no justice," he told
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question: Who was charged in two killings?, answer: Walter E. Ellis, | question: How many killings has Ellis been charged in so far?, answer: nine | question: how many women were killed, answer: nine | question: when were the women killed, answer: The homicides occurred between 1986 and 2007, | question: Who was the DNA on the bodies matched to?, answer: Walter E. Ellis, | question: In what year did the killings start?, answer: 1986. | question: The women were killed when?, answer: between 1986 and 2007, | question: Who was the DNA found on bodies of nine women matched to?, answer: Walter E. Ellis, | question: who is the suspect, answer: Walter E. Ellis, | question: what has ellis been charged with?, answer: two counts of first degree murder | question: when were they killed, answer: over 21 years, | question: who was DNA found on bodies of nine women matched to?, answer: Walter E. Ellis, | question: when were the women killed?, answer: between 1986 and 2007, | question: where did the murders take place, answer: Wisconsin,