Mother of Miami man who killed wife, stepdaughters testifies 'he is my son' in death penalty trial

"Alberto is my son; I'm not justifying what he did. I'm not making up any excuses, but he is my son," Mercedes Pedraza testified in court Tuesday during the penalty phase of her son's trial.

Alberto Sierra, 42, became emotional as his mother took the stand. Sierra pleaded guilty in August to the 2012 murders of his estranged wife, 29-year-old Gladys Machado, and her two daughters, 6-year-old Julia Padrino and 3-year-old Daniela Padrino, after suffocating all three with a plastic bag. A jury will now decide whether he will face the death penalty.

On Tuesday, Pedraza testified about Sierra's upbringing, past relationships, and the lasting impact on his behavior after he sustained a traumatic brain injury when he was hit by a car at age 12. She also recalled what Sierra told her the day they went to the police station following the murders.

"Mami, everything is going to be okay, don't worry," Pedraza testified that he said. "I hug him, I give him a kiss, and that was it."

The defense argues that the childhood accident left Sierra with a traumatic brain injury that altered his behavior and decision-making.

Dr. Erin Bigler, a psychologist specializing in brain-behavior, testified via Zoom while brain scans of Sierra were shown to the jury.

"With impact injury, in a motor vehicle accident, the frontal lobe is so vulnerable," Bigler testified. "Because you can have the initial impact that can cause fractures, but then, you have the body hitting the ground as well. So, you get secondary injuries, and the brain is going back and forth."

The trial is set to resume Wednesday morning.