Story highlights Sara Yarborough was killed in December 1991

A DNA sample matches descendants of a 17th-century Massachusetts family

"The most important thing is having a last name," the DNA analyst says

DNA may help Seattle-area sheriff's deputies find a suspect in a 20-year-old killing after a comparison with genealogy records connected a crime-scene sample to a 17th-century Massachusetts family.

The DNA sample was taken in the death of 16-year-old Sarah Yarborough, who was killed on her high school campus in Federal Way, Washington, in December 1991. The King County Sheriff's Office has circulated two composite sketches of a possible suspect -- a man in his 20s at the time with shoulder-length blonde or light brown hair -- but had been unable to put a name to the sketch.

In December, though, the department sent the DNA profile to California-based forensic consultant Colleen Fitzpatrick. Fitzpatrick compared the profile to others in genealogy databases and found the closest match was to the family of Robert Fuller, who settled in Salem, Massachusetts, in 1630 and had relatives who came over before him on the Mayflower.

While the descendents of Robert Fuller are likely to number in the thousands after nearly 400 years, geography and physical characteristics can help detectives narrow their search, Fitzpatrick said. In fact, Fitzpatrick said, since the DNA trace follows male descendants, there was "a high degree of probability" that the man police are looking is named Fuller.

"The most important thing is having a last name," Fitzpatrick told CNN. "People get excited about having a Mayflower connection, but the most important thing is having a probable last name for this guy."

King County investigators disclosed the test results Monday.

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Fitzpatrick said the DNA she used came from one of several major collections of genetic profiles, a practice she said was "really hot these days for genealogy." She said the people who donated DNA profiles to the database had either done their genealogy or had their DNA tested to trace their connections.

"It allows you to connect with relatives you can't trace through traditional documentation," she said.