A Miami-Dade man has pleaded guilty to the horrific murders of his wife and her two young daughters nearly 14 years ago and will now face a possible death sentence. Alberto Sierra, 42, pleaded guilty on Friday to three counts of first-degree murder, three counts of kidnapping, two counts of abusing a human body and one count of armed burglary. According to an arrest affidavit, Sierra suffocated Machado with a plastic bag "and subsequently sexually assaulted her," then let one of the girls out of her bedroom and suffocated her. The bodies of Machado and her daughters were found three days later in a closet at the home, police said. Authorities had questioned and released Sierra but he later gave a full confession to the murders, the affidavit said.