Wait a minute. Did she do the cop’s job?
No, they had the guys DNA and they had been continually looking for a DNA match for years. But one day, his sister put her DNA on a web site. Now she was close enough to her brother's that the police then got DNA from the killer. His DNA matched that found at the murder scene. Hello prison!
It doesn't seem she realized that her DNA would eventually nail her brother. The fact that they kept checking means that the cops never quit.