Asked what could have sparked Chicago’s 16-month-old surge in gun violence, Derek Brown points to the city’s November 2015 release of a police dashcam video that shows a white police officer fatally shooting a black teen named Laquan McDonald.

Brown, who teaches boxing to at-risk West Side youths, recalled how the video affected his students and their peers.

“They were mad and didn’t know how to channel that anger,” recalled Brown, 40, who said he climbed the ranks of the Vice Lords before leaving gang life a decade ago.

“Instead of them lashing out on the authority figures, they were lashing out on each other. It’s just like — if my parent whoops me in the house, just whoops me for no reason — it’s easier for me to lash out on my little sister than to go at my parent.”

The video also sent a message about using guns to resolve conflicts, Brown said.

One of his students, a 20-year-old awaiting trial on a gun charge, said he watched the video repeatedly and saw a takeaway: “He just shot someone right on camera and he’s finnin’ to get away with murder,” the student said, speaking on condition he not be identified. “So I can do this and not get caught ... and not go to jail too.”

Brown said the McDonald video sparked a sort of violence that quickly took on a life of its own. “Once one corner shoots at one corner,” he said, “the other corner is going to bust back.”

It may seem far-fetched to blame a video for a shooting surge that has killed or injured roughly 5,300 people since it began in January 2016. But some criminologists are taking the idea seriously. And a WBEZ analysis of Chicago data has found a disturbing trend in calls to 911 that bolsters Brown’s view.

That view is but one of many explanations about what sparked the city’s shooting surge. As part of the WBEZ project Every Other Hour, this report provides a look at those theories and delves into competing versions of what can be called “the Laquan effect.”