The penalty phase of the Adam Matos murder trial begins on Monday. Last week, Matos was convicted of four counts of first degree murder for the deaths of  his ex-girlfriend Megan Brown, her new boyfriend Nicholas Leonard, and her parents Margaret and Gregory Brown in 2014. The penalty phase began Monday , and closing arguments will begin Tuesday morning at approximately 9:30 am EST. The jury will then have to decide whether to sentence Matos to death or life in prison.

Prosecutors argued during the main part of the trial that Matos first had a domestic dispute with Megan Brown on August 28, 2014, but left when his son woke up. He returned later that day and murdered her and the others. The next day, Matos allegedly started selling the Brown family’s belongings, including animals that the family owned.

Matos testified in his own defense during the trial, admitting to the killings but saying he acted in self-defense. He claimed all four were out to kill him, so he killed them to protect himself.

On Monday, the prosecution called witnesses to testify as to the nature of the victims’ fatal injuries. The defense introduced testimony from Matos’ family members, including his mother and aunt. Their opening statement focused on Matos’ upbringing and development, as well as his love for his son Tristan.

Stay with LawAndCrime.com and the Law & Crime Network for continuing coverage of the trial.