In the early hours of Dec. 3, 2016, 19-year-old Sarah Stern's car was found abandoned on a bridge in New Jersey, keys dangling from the ignition inside. It seemed to be suicide. The car had not been broken into and there were no signs of a struggle. Dive teams searched the river below, while helicopters skimmed the shores. There was no sign of her. Now, her friend from childhood, Liam McAtasney, has been convicted of killing her.