The Latest: Expert explains PCP effect on Laquan McDonald

The Latest on the trial of Chicago police Officer Jason Van Dyke, who is charged with murder in the shooting death of Laquan McDonald (all times local):

11:45 a.m.

A pharmacologist testifying in the trial of a white Chicago police officer charged with murder in the shooting of Laquan McDonald says PCP in the black teen's system could have caused aggression, rage and hallucinations.

James Thomas O'Donnell said during Van Dyke's murder trial on Thursday that that someone with as much of PCP in his system as McDonald had in his bloodstream could have a "feeling of omnipotence." O'Donnell said the person could feel as if he has "superhuman powers." He says that could put a person at risk of harming himself or others around him.

Other witnesses have testified that McDonald refused to drop a knife as police ordered and that McDonald stabbed the tire of a police vehicle. O'Donnell said such "violent rage behavior" could be explained by having PCP in his system.

Under cross examination, O'Donnell acknowledged that he had no information that Van Dyke knew McDonald had PCP in his system when he shot him 16 times on the night of Oct. 20, 2014.

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11 a.m.

A woman is telling the jury in Chicago police Officer Jason Van Dyke's murder trial about an encounter she had with the teen Van Dyke killed hours earlier that concerned her enough to call police.

Yvette Patterson is the latest witness called by defense attorneys who want jurors to know about angry and sometimes violent encounters that black teenager Laquan McDonald had with people. Others have included current and former employees at the county's juvenile detention facility when McDonald was there.

Patterson said Thursday that when she got to her home early on Oct. 20, 2014, McDonald was sitting on the stairs. She said he walked to her vehicle and said he wanted to use it. She said that when she told McDonald he could not use her car, he "said OK and started laughing."

Still, she said she was concerned enough about her safety to call 911.

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11:57 p.m. Wednesday.

Lawyers for a white Chicago police officer who shot black teenager Laquan McDonald to death in 2014 are scheduled to call more witnesses as they defend him against murder and other charges.

Thursday will be the fourth day that Jason Van Dyke's attorneys present evidence to Cook County jurors.

Defense attorneys are trying to show it was reasonable for Van Dyke to have perceived McDonald as a threat. The officer shot the teen 16 times as he walked away carrying a knife.

Several defense witnesses have testified about violent encounters McDonald had with authorities at a juvenile detention facility months earlier. And a truck driver testified that McDonald tried to stab him the night of the shooting.

Prosecutors rested their case last week but could call more witnesses after the defense rests.