A boy is dead and his mother and brother are in critical condition after an apparent road-rage shooting in a Colorado parking lot, authorities said.

Suspect Jeremy Webster, 23, is in custody, according to the Westminster Police Department, just outside of Denver.

The deadly shooting took place Thursday afternoon at a Westminster business complex, police said.

An adult man, who was not related to the other victims, was also shot in the afternoon incident and is expected to survive, authorities said.

Further details of the incident were revealed in a search warrant filed against Webster. According to the warrant, Webster got into an argument with 41-year-old Megan Bigelow stemming from "some sort ofroad rageincident." Webster followed Bigelow in his car to an office complex, where Bigelow and her three children -- 8, 12 and 13 -- exited the car and got into a further argument, the warrant shows.

Webster allegedly shot Bigelow and then targeted the children, the warrant says. The 13-year-old boy was struck and fell to the ground and Webster allegedly stood over the boy and shot him again. The child was killed.

The suspect apparently didn't know any of the victims, police said.

He faces charges including first-degree murder after deliberation with intent, police said.

Bigelow also opened fire on an eyewitness in his car who was struck and injured, the warrant alleges.

"Jeremy stated that he has mental health issues and just started a newly prescribed medication today," according to the affidavit.

The warrant states Webster admitted to shooting the mother, her kids, and the onlooker. (ABC News)

•Jeremy Webster, 23, has been charged with murder for allegedly shooting a 13-year-old boy in a road rage incident on Thursday, June 14, 2018.