FORT LAUDERDALE, Florida (AP) — Florida school shooter Nikolas Cruz as a toddler was intellectually and physically behind other children, which caused him to isolate himself and hit and bite to get what he wanted, a daycare administrator and former neighbour testified Tuesday at his penalty trial for mass murder.

Cruz’s attorneys began the second day of their defense by building on testimony that his birth mother’s cocaine and alcohol abuse during pregnancy left him severely brain damaged, putting him on a road that led to him murdering 14 students and three staff members at Parkland’s Marjory Stoneman Douglas High School on February 14, 2018.

They are trying to persuade his jury to sentence him to life without parole instead of death. Cruz, 23, pleaded guilty in October to the murders and the trial is only to determine his sentence.

Anne Fischer, who ran the daycare center Cruz attended from about age 1, said he did not progress as fast as other children and was smaller. She said while the other toddlers could ask for their water cups and use a spoon, Cruz could not. She said he would fall down when he tried to run and his head and ears seemed disproportional to his body.

“He isolated himself a lot. He would sit in the corner and observe,” Fischer said.

He pushed other kids because he “didn’t know how to express himself,” she said. “If someone else had a toy that Nikolas wanted, he would just go up and grab the toy and hit the child’s hand to get the toy or the object. If a teacher was trying to work with him to get him to use his spoon or not his hand, he would hit the teacher’s hand away.”

She said Lynda Cruz, his adoptive mother, was loving toward Nikolas and tried to do the best she could, but was slow to admit he had problems.

She said that since the shooting, she sometimes feels a bit guilty, wondering if there was something she could have done “so he could be a better person.”

The defense is trying to overcome the prosecution’s case, which featured surveillance video of Cruz mowing down students and staff as he stalked a three-story building for seven-minutes, photos of the aftermath and a jury visit to the building.

For Cruz to receive a death sentence, the jury must be unanimous. If one juror votes for life, that will be his sentence.