Willa Wertheimer's waited 36 years to find out what happened to her half-brother.

Now she finally has the answer after DNA she submitted in 2011 came up with a match as part of the cold case investigation to identify remaining victims of serial killer John Wayne Gacy.

Wertheimer's relative, named in media reports as 16-year-old Andre Drath, was not one of Gacy's victims but was found shot to death in San Francisco in 1979.

His identify remained a mystery until Wertheimer submitted her DNA when police announced they were reopening the investigation to put names to the remains of eight of Gacy's victims.

"Believe me, although I'm terribly sad, the knowing is so much better. No matter how invisible you think your relative may be, there's likely a good amount of information out there that can be found," she said.

Police say the submission of DNA from relatives who fear missing loved ones may be among the eight unidentified Gacy victims has also identified 12 more people who had vanished without trace.