Investigators from the FBI linked a New Jersey attorney to a series of violent rapes in Boston after tracking down his relative's DNA on a commercial genealogy database.
Matthew Nilo, 35, was arrested last week on suspicion of raping three women and sexually assaulting a fourth in 2007 and 2008.
Police took samples from the three women who were raped in Terminal Street, in Boston, at the time of the incidents and processed the glove of a fourth victim who poked her assailant in the eye while wearing the garment.
All three matched the same profile, leading officers to believe that the same man committed each of the assaults.
The FBI confirmed 15 years later that the DNA belonged to Nilo after comparing the samples to one from a glass he drank from at a corporate event, but there were multiple hurdles they had to first overcome.
Matthew Nilo, 35, denied attacking four women in Boston in 2008 and 2007 during his appearance in Suffolk Superior Court on Monday
Police took samples from the three women who were raped in Terminal Street, in Boston, penipu at the time of the incidents and processed the glove of a fourth victim who poked her assailant in the eye while wearing the garment
The investigation initially stalled because the DNA obtained from each of the women failed to flag any potential matches on the federal CODIS system.
Officers kept the case open, using the Sexual Assault Kit Initiative - a federal program designed to help process a backlog of rape kits - to reinvestigate the incidents.
Boston Police Department doesn't have a backlog of rape kits but has instead used the initiative and a $2.5million federal grant to re-examine 'unsolved cases that present the greatest threat to public safety.'
Cops requested the DNA be cross-referenced by the FBI using 'forensic investigative genetic genealogy' in October last year.
Officers from the BPD submitted the DNA samples obtained from the three women to GEDMatch and Family Tree DNA, two of the only genealogy websites which allow law enforcement access to their databases.
Because the databases are so small, the FBI could only search 'about two million people', meaning they had to either 'get lucky or be really skilled.'
Consumers using the sites must consent before their information is shared with law enforcement, and they use the sites to trace their ancestry or locate other relatives.
GEDMatch and Family Tree DNA then provide a list of relatives and the percentage of DNA they share with the sample submitted by the police - which led them to Nilo in April this year.
The FBI confirmed 15 years later that the DNA belonged to Nilo after comparing the samples to one from a glass he drank from at a corporate event
His fiance Laura Griffin was seen gripping rosary beads during his court hearing in Suffolk Superior Court on Monday
<video controls="" class="video-js vjs-default-skin" website website Reynolds for DailyMail.