CHICAGO (CBS) — On the day Laquan McDonald would have turned 21 years old, his troubled life likely will once again be the focus of testimony at the murder trial of Chicago Police Officer Jason Van Dyke, charged in the teen’s fatal shooting four years ago.

The defense plans to call several more expert witnesses, including a ballistics expert, a use-of-force expert, and a video expert who will testify about a video animation created by the defense to show the shooting from Van Dyke’s perspective.

Van Dyke’s defense team began presenting its case on Monday, and three witnesses testified about encounters with McDonald long before the shooting, describing hostile, antagonistic, and violent behavior.

One Cook County Sheriff’s officer described a 3- to 5-minute struggle to handcuff McDonald in a holding cell at the Juvenile Court.

“I helped my partner grab him, so we could get him to the ground, so we could get some control of him, because at this point he was resisting. He didn’t want anything to do with us. He balled up. We finally got him to the ground, and he was still yelling and screaming. Wouldn’t give up his hands. Kicking,” Officer Joseph Plaud said.

However, all three witnesses also acknowledged Van Dyke had no knowledge about any of the incidents they described.

Chicago police Officer Jason Van Dyke stands in court during his trial on murder charges at the Leighton Criminal Court Building September 24, 2018 in Chicago, Illinois. Van Dyke is charged with shooting and killing black 17-year-old Laquan McDonald, who was walking away from police down a street holding a knife. (Photo by Antonio Perez-Pool/Getty Images)

The defense has argued the shooting is a clear case of self-defense, painting McDonald as dangerous and violent. Van Dyke’s attorneys are expected to take more than a week to put on their case.

Their first defense witness on Monday was Dr. Shaku Teas, a forensic pathologist hired by the defense for about $9000 to review and analyze the autopsy conducted by the Cook County Medical Examiner’s office, where she used to work.

Teas testified that McDonald likely died from a single gunshot wound to his chest. She also said, in her opinion, McDonald likely was standing when he was hit by most of the 16 shots Van Dyke fired. She maintained the 17-year-old ward of the state was at least partially facing Van Dyke when he was first shot.

“He had to be facing him at least partially. At least his chest was facing him at that point,” she said.

McDonald’s supporters have planned two events to celebrate what would have been his 21st birthday on Tuesday, including a vigil outside the courthouse at 6 p.m.