CHICAGO — Officer Jason Van Dyke asked 12 jurors to trust his memory, not a widely circulated dashboard camera video, to know what really happened the night he shot Laquan McDonald 16 times.

The jurors chose the video.

On Friday afternoon, after less than eight hours of deliberating, the jury convicted Officer Van Dyke of second-degree murder and 16 counts of aggravated battery with a firearm in the death of Laquan, a black teenager who was carrying a knife but veering away from the police.

Most of the jurors stayed behind in the courtroom to speak to reporters after the verdict, as Officer Van Dyke, who is white, was booked into jail. They said they found the officer’s description of the Oct. 20, 2014, shooting to be contradictory, overly rehearsed and simply not believable. And they called into question officers’ tried-and-true strategy of providing tearful testimony to overcome damaging video evidence when charged in a shooting.

“It seemed kind of like he was finally giving the play after they had been rehearsing with him for weeks,” said one juror, a white woman, who noticed Officer Van Dyke “staring at us, trying to win our sympathy” when he testified.