Alberto Sierra Said He Looked Away as Wife Struggled to Breathe, Detective Tells Death Penalty Jury

Alberto Sierra told detectives he looked away while holding a plastic bag over his estranged wife's face as she struggled to breathe, a Florida jury heard in the penalty phase of his case in Miami on Monday, 5 October. Jurors were told he later used the same bag to suffocate her two young daughters.

Sierra, 42, has pleaded guilty to murder, burglary, kidnapping and abuse of a dead body in connection with the 2012 deaths of his estranged wife and her two children.

Prosecutors are seeking the death penalty, while his lawyers are arguing for life imprisonment without parole. The hearing is now focused solely on punishment rather than guilt.

Jurors heard that Sierra initially denied involvement before confessing after detectives confronted him with DNA evidence linked to one of the children. The detective said Sierra's demeanour changed after the evidence was raised and that he lowered his head, clasped his hands and began to quiver before agreeing to explain what had happened.

Alberto Sierra Confession Played for Jurors

The detective told the jury that Sierra described an argument with his estranged wife after she rejected two telephone calls while the family was returning from a shopping trip.

Although the couple were separated, Sierra admitted becoming jealous and confronting her about another man, according to the testimony.

Sierra said a struggle over a knife followed before he took control of the weapon. He told investigators that he drove his wife and the two girls back to the home and warned them that he would not hurt them if they did not scream.

The detective said Sierra then locked the children in a bedroom before taking his wife into the master bedroom. Sierra told investigators that he tied her wrists behind her back and demanded the passcode to her phone.

After gaining access, Sierra searched her calls, messages and emails. The detective testified that Sierra then pinned his wife down and held a plastic bag over her face. Sierra said she kicked and struggled for about a minute as he restrained her. He told investigators that he turned his face away so he would not have to watch her struggling to breathe.

Jurors also heard the detective recount Sierra's statement that he later suffocated both girls with the same plastic bag. The detective further testified that Sierra admitted sexually abusing his wife's body after her death. He also said Sierra admitted sexually abusing one of the girls after killing her.

Prosecutors Challenge 'Broken Brain' Defence

The prosecution used Sierra's account of his actions after the killings to challenge the defence's claims about his brain damage. The detective said Sierra admitted gathering items from the bedroom and his wife's belongings before cleaning the home in an effort to destroy evidence tying him to the scene.

Asked whether Sierra had devised the clean-up himself, the detective said that was Sierra's intention, describing it as an attempt to 'clean up his tracks'. A prosecutor then asked whether Sierra had ever explained how his 'broken brain' allowed him to carry out the clean-up.

The wording echoed the defence's opening statement. Sierra's lawyers have described him as having a 'broken brain' and argued that he suffered severe brain damage resulting in the loss of part of his frontal lobe.

Those claims form a central part of the defence argument against execution. His lawyers are asking jurors to support life imprisonment without the possibility of parole instead.

Prosecutors, meanwhile, have focused on Sierra's own description of restraining the victims, searching his wife's phone and taking steps to clean the scene afterwards.

Alberto Sierra Jury Weighs Death Against Life Without Parole

Because Sierra has already pleaded guilty, jurors are not being asked to determine whether he committed the crimes. Their task in the current proceedings concerns the punishment he should receive.

Monday's testimony placed Sierra's confession at the centre of that decision. Jurors heard how his account changed after detectives confronted him with DNA evidence and how he described the actions leading up to and following the killings.

The prosecution has highlighted those details as jurors consider a possible death sentence. The defence, by contrast, is asking them to weigh Sierra's reported brain damage and choose life imprisonment without parole.

The penalty phase is continuing as jurors hear further evidence from both sides. They must ultimately weigh the circumstances of the killings against the defence's mitigation case when considering whether Sierra should face death or spend the rest of his life in prison without parole.