<p>Columbus Police agree to speak with Mary's identical twin sister, Martha Petry, and reveal they are waiting to submit DNA evidence for forensic genealogy analysis. First, they're working to rule out two other suspects. James Renner, a true crime author and founder of the nonprofit Porchlight Project, says a window for solving the case may be closing as forensic genealogy becomes increasingly regulated.</p>

Columbus Police agree to speak with Mary's identical twin sister, Martha Petry, and reveal they are waiting to submit DNA evidence for forensic genealogy analysis. First, they're working to rule out two other suspects. James Renner, a true crime author and founder of the nonprofit Porchlight Project, says a window for solving the case may be closing as forensic genealogy becomes increasingly regulated.

6. Behind the “Blue Wall” (Sort Of)

In 1970, Mary Petry and Bill Sproat, two university students in love, were murdered in a Columbus, Ohio apartment. The crime was so brutal it drew comparisons to the Manson murders of the previous year. The case has never been solved. Host/Producer Justin Glanville and the sisters of the two victims track down friends, witnesses to the original investigation and the Columbus police to understand why the case remains unsolved, despite the existence of solid DNA evidence and the fact that police say they have a person of interest. Along the way, the three explore who really owns DNA collected at crime scenes – families or police? – and what it takes to bring new attention to a 53-year-old cold case in an era when police departments are struggling to attract new recruits.

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6. Behind the “Blue Wall” (Sort Of)

6. Behind the “Blue Wall” (Sort Of)

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