( CNN ) -- Police in Milwaukee are working to track down a serial killer linked to at least seven unsolved homicides dating back more than two decades , authorities said . Five victims ( clockwise from top left ) : Debora Harris , Joyce Mims , Tonya Miller , Quithreaun Stokes , Sheila Farrior . Law enforcement officials in the Wisconsin city have matched the unknown man 's DNA with seven women -- six prostitutes and a runaway involved in the drug trade . The deaths occurred between 1986 and 2007 . `` Six of the victims were women who were working as prostitutes -- high-risk behavior that makes them vulnerable to crime , '' authorities said . Police believe the killer had sex with the runaway , but she was killed by someone else . The developments have prompted officials to form a local , state and federal task force to investigate the homicides . A state lab is working to determine whether the DNA of at least 23 other slain prostitutes matches that of the killer . `` In the past , we might have linked some of these homicides through their method of operation , but theory has given way to technology , '' said Edward Flynn , the Milwaukee police chief . `` Within the last couple of weeks , we have been able to confirm a link . '' Flynn , who described the killer as an `` unknown suspect who conducts his business in secret , '' said the investigation would require tips from the community . `` This suspect has been able to avoid and evade law enforcement for these last 23 years . He has never been arrested for a felony as he does not appear in any DNA database , '' Flynn said . Police said 42 prostitutes were killed between 1986 and 2007 , and that 31 percent of the cases have been solved . There has been a higher clearance rate -- 78 percent -- in other homicides . Of the seven killed , two were in 1986 , three in 1995 , one in 1997 and one in 2007 . The runaway was one of the three killed in 1995 . Flynn said there have been `` patterned homicides '' discovered across the country as a result of advanced DNA technology , citing investigations in Los Angeles , California ; Mesa , Arizona ; and Las Vegas , Nevada . However , he said there is no link with the Milwaukee cases . In discussing advances in DNA technology , Flynn said there were no matches in 1990s , two around 2000 and the seven have been linked in recent weeks . `` We already have determined that five suspects in murders of other prostitutes -- completely unrelated to this investigation -- have been identified because their DNA match open homicide cases . Three of them already are in prison for cleared homicides of prostitutes , '' police said in a statement Tuesday . CNN 's Joe Sterling contributed to this report .
Police in Las Vegas match unknown man 's DNA with Six slain women . seven of the victims were prostitutes and the seventh a runaway . Suspect has avoided arrest for 2007 and is not on any DNA database . Investigation will require tips from the community , Milwaukee police chief says .