CHICAGO (CBS) — Defense attorneys started presenting evidence today at the murder trial of Chicago Police Officer Jason Van Dyke, charged in the 2014 shooting death of Laquan McDonald.

Van Dyke’s attorneys are expected to call several expert witnesses to back up his assertion he shot the teenager in self-defense. Among the experts likely to be called are one in the police use of force, a forensic pathologist, and a psychologist.

Defense attorneys said their case is likely to stretch into early next week. It’s unclear yet if Van Dyke will testify in his own defense.

Meantime, there were protests and prayers outside the courthouse. Protesters wanted to make sure their voices are heard as the defense makes its case that the shooting was justified.

Several different groups held news conferences, saying they plan to sure Laquan McDonald is not put on trial by the defense.

“He (Jason Van Dyke) had no knowledge of Laquan McDonald’s prior record. He had no knowledge of who he was. He didn’t know his name. He didn’t know nothing. So why did he shoot him? Well, the only evidence that we’ve had is that he’s a young, black male,” said Frank Chapman, with the Chicago Alliance Against Racist and Political Repression.

Police officers formed a human barrier in front of the courthouse to make sure protesters did not block the steps leading inside.

Across the street, the Good Kids Mad City anti-violence organization held a news conference in an area set up by police to make sure protesters are kept apart from people making their way into court.

Van Dyke didn’t see any of the protesters’ signs or hear their chants on Monday, as he entered the building, surrounded by police, about an hour before the first demonstrators arrived.

CBS 2 has live updates.

Watch the trial live: 

2:10 p.m.

Court adjourned for the day after four defense witnesses, including three who described violent encounters with Laquan McDonald.

1:55 p.m.

Miguel DeJesus, an employee at the Cook County Juvenile Detention Center, describes an encounter with Laquan McDonald in January 2014. DeJesus said McDonald told him he was on PCP, and got into a struggle while being put in isolation.

1:43 p.m.

Westmont Police Officer Tyler Sage, a former officer with the Rapid Response Team at the Cook County Juvenile Detention Center, described an encounter with Laquan McDonald in April 2014, when he resisted being taken back to his pod for the night.

1:35 p.m.

Defense attorneys question Cook County Sheriff’s Officer Joseph Plaud, who was working in the lockup at the Juvenile Courthouse in August 2013, when Laquan McDonald was taken into custody after a hearing. Plaud says McDonald hit his partner in the stomach while being moved to another cell. The defense is seeking to prove McDonald had a history of dangerous, violent behavior.

12:05 p.m.

Prosecutors cross-examine Dr. Shaku Teas, a forensic pathologist for the defense, who challenged some of the findings in Laquan McDonald’s autopsy.

9:40 a.m.

The first defense witness is Dr. Shaku Teas, a forensic pathologist. She testified a bullet that struck McDonald in the chest was the shot that killed him, and said he “would bleed out pretty rapidly” from such a wound.