In Wisconsin's capital, relationships, demographics, tradition keep police protests peaceful

Demonstrators walk in a tunnel under the Monona Terrace Convention Center while making their way along John Nolen Drive during a rally for Tony Robinson in Madison, Wis., Wednesday, May 13, 2015. Dane County District Attorney Ismael Ozanne said Tuesday, May 12, that he wouldn't file charges against Madison Officer Matt Kenny in the March 6 death of Robinson, saying the officer used lawful deadly force after he was staggered by a punch to the head and feared for his life. (John Hart/Wisconsin State Journal via AP) (The Associated Press)

A woman is led away in handcuffs by a police officer during a protest in Madison, Wis., Wednesday, May 13, 2015. Dane County District Attorney Ismael Ozanne announced Tuesday that Madison police officer Matt Kenny would not face charges for the shooting death of unarmed Tony Robinson in March. (M.P. King/Wisconsin State Journal via AP) (The Associated Press)

Former Alder, Barbara Vedder is stopped by a police officer from crossing Doty Street during a protest in Madison, Wis., Wednesday, May 13, 2015. Dane County District Attorney Ismael Ozanne announced Tuesday that Madison police officer Matt Kenny would not face charges for the shooting death of unarmed Tony Robinson in March. (M.P. King/Wisconsin State Journal via AP) (The Associated Press)

When a white police officer killed an unarmed biracial teen in Wisconsin's capital city, the shooting heightened tensions and stirred up some protests.

But no one has hurled so much as a pebble, broken anything or thrown any punches. The approximately two dozen arrests so far involved protesters blocking traffic.

Instead, existing relationships, local traditions and cooler heads helped keep the streets of Madison peaceful — at least so far.

Officer Matt Kenny killed 19-year-old Tony Robinson on March 6. On Tuesday, a prosecutor announced that the officer would not be charged.

Police credit their longstanding relationships with black leaders. Chief Mike Koval reached out to Robinson's family personally, even praying with Robinson's grandmother in her driveway.

The ultra-liberal city has a long tradition of accommodating and encouraging political demonstrations.