Jayden Perkins was stabbed to death, while trying to protect his mother in March of 2024.
Crosetti Brand, 39, is facing several charges, including first-degree murder, for the death of the young boy.
Perkins' mother, Laterria Smith, who was pregnant at the time, was also seriously hurt in the attack.
Brand was released on parole the day before the attack.
The 39-year-old suspect is representing himself.
Under tight security in the courtroom Tuesday, jurors learned more about the day Perkins was killed.
A neighbor who came to the aid of Smith and her son testified.
"It was shocking; I didn't know it was that bad when I opened that door," Lilliam Rodriguez said.
Rodriguez testified that she heard Smith, who was pregnant, and saw Smith's front door open.
Rodriguez asked if Smith needed help.
And as Rodriguez opened the door, she told jurors she saw Smith and Perkins on the floor.
"She was bleeding from the neck. It was really bad," Rodriguez said. "I saw the other boy lying on the floor near the door."
Rodriguez shared it was difficult to testify, but she wanted to support Smith.
"I'm a mother. I'm on her side because I know it's not right," Rodriguez said.
Smith's former fiancé testified about the day of the attack.
Kassidy Miles testified that the couple's then-5-year-old son was at the apartment during the attack, but was unharmed. The 5-year-old called Miles at work in a video call on an iPad.
"He told me, 'Jayden and mommy are dead.' I cried and fainted and hollered and screamed," Miles said.
Perkins died from a stab wound to the chest.
The boys' mother survived 11 stab wounds.
Brand questioned Miles under cross-examination. Miles testified he didn't know of relationships Smith was having, and that the couple is now not engaged.
Miles declined to comment as he left court Tuesday afternoon.
Despite Brand's right to defend himself at trial, his movements are very limited. There have been extra officers and rules in court for security.
The trial resumes at 10:30 a.m. Wednesday.
Smith was the first to take the stand on Monday.
The trial is expected to last about three weeks.
Smith filed a wrongful-death lawsuit, claiming that her son's killing was preventable.
The death of Perkins and a woman whose husband was on electronic monitoring when he reportedly killed her on the Northwest Side have led to the Cook County State's Attorney's Office making domestic violence cases a priority.
You can contact the Illinois domestic violence hotline at 1-877-863-6338 click here for more information.