Defense attorney Khurrum Wahid acknowledged the killings’ brutality Tuesday while asking jurors to consider Sierra’s life history and keep life imprisonment in view. Sierra, 42, confessed to killing his estranged wife, Gladys Machado, 29, and her daughters, Julia Padrino, 6, and Daniela Padrino, 3, on Nov. 10, 2012.

“He admits that he did this monstrous act,” Wahid said. He reminded jurors they had pledged during jury selection to remain fair and consider life as a possible punishment, despite the evidence and their emotions.

Wahid pointed to a serious head injury Sierra suffered in a car crash in 1996, when he was 12. Defense experts testified that the injury caused structural damage to his brain and could have affected his behavior, personality and ability to plan and make decisions.

“Nobody chooses to have a skull fracture when they are 12 years old,” Wahid said, arguing that the injury marked a turning point in Sierra’s life.

The defense also asked jurors to consider Sierra’s mother, a Cuban immigrant who raised two sons alone while working two jobs. Wahid said she tried to help her son but the family did not recognize that his behavioral changes might require specialized intervention.

“The choice here is a moral choice that is before you,” Wahid told jurors, urging them to choose life without needing to justify that decision to anyone else.

Lead prosecutor Abbe Rifkin argued Monday that the killings’ severity warranted a death sentence. She described Machado’s injuries and said the victims were suffocated with a yellow plastic Sedano’s bag. Rifkin characterized the killings as “heinous, atrocious and cruel.”

The jury heard the closing arguments Monday and received final instructions from the judge Tuesday. Its decision will determine whether Sierra receives a death sentence or life in prison without parole.