His sister, Victoria Castillo, took the stand and talked about her and her brother's upbringing. Fighting back emotions, Victoria described her father as abusive and controlling.
"My mother would try to talk to us to teach us," Victoria Castillo explained. "My dad would get very angry very easily [sic] to hit us."
Alvaro Castillo claimed he was abused by his father and that's why he shot him to death.
She recalled her brother's first suicide attempt at age 15 and his growing obsession with death.
But his accumulation of weapons -she said- remained a well kept secret until their parents confronted him.
"He got very nervous, almost like a child when you are trying to take something they love away from them," Victoria said.
Alvaro and Victoria's mother also took the stand on Tuesday. She described the shock she felt when she learned her husband was dead and her son was the alleged killer.
"Why did you kill him, he said everything's going to be fine, dad is in heaven now," Castillo's mother Vicky Castillo told the court.
His mother also detailed a family history of mental illness and said her son believed he was following orders from God.
"He said he didn't do anything wrong, Victoria and I looked at each other and we knew he was very sick," she said.
On Wednesday, the defense will continue making its case for why Castillo should not go to prison.