Family ancestry programs using DNA changed that. One of the DNA registries noted that a sample sent to it matched DNA that had been left behind on Sophie's body (I do not know if this was part of a routine procedure by the company or a more targeted search). It turns out that a close relative to the murderer had submitted the DNA sample. Sophie's murderer tried have the case thrown out under the idea that his DNA was taken without his permission, but as the DNA was actually a relative's and was given voluntarily, he was ultimately found guilty.
Today, 29 and a half years later, Sophie's murderer was officially sentenced to 75 years in prison. While this does not bring Sophie back, I hope that it gives her family a sense of peace and closure. It also fully lifts the veil of suspicion that other men, one of whom I knew personally, had to deal with all of this time due to their connections to Sophie. Oddly, news of the sentencing also lifted an anger and frustration that I did not realize that I had been carrying all this time.
Rest in peace, Sophie.