welcome back to "dateline extra." so far jason young's testimony seemed to be answering years of questions. when asked by his attorney, jason admitted cheating on his pregnant wife, michelle. more than once. even so, the defense pointed out infidelity did not make him a murderer. now it was the prosecution's turn to cross-examine the witness. and they'd start by attacking jason's alibi. but with no forensic evidence tying him to the crime scene, could they convince the jury that jason was the killer? continuing with our story, here's keith morrison. >> reporter: it was riveting. almost five years of silence about his wife's murder broken here in this courtroom. >> i love cassidy.