A bombshell witness upends the Merritt murder trial, claiming someone else confessed to the McStay murders; Merritt's girlfriend gives him an alibi, but the prosecution attempts to discredit her on the witness stand.

Police investigate other suspects, including a business associate taking money, an ex-boyfriend still in love with Summer McStay and a new husband with a violent past; footage of a truck leaving the McStay house may reveal the killer.

Merritt's phone pings near the desert graves, and authorities wonder whether he buried the bodies or merely visited a sister; prosecutors suggest he tried to delete financial records to cover his tracks; a defense attorney takes a sudden leave of absence.

New DNA found in the graves may reveal who murdered the McStays; the defense questions Joseph's brother on his whereabouts at the time of the murders, and they cannot locate the suspect they believe may have ties to the killings

If Merritt testifies, the jurors will learn about his criminal past; the defense and prosecution present their final arguments with closing statements, and it's now up to the jury to determine guilt or innocence.