Sunday’s deadly shootout between rival biker gangs in front of a Waco restaurant may have first begun, police believe, with an argument over a parking space.

A fight broke out Sunday afternoon between at least five biker gangs outside a Waco Twin Peaks restaurant, leaving nine people dead and 18 injured. Police arrested 170 suspects in connection with the fight yesterday.

Based on witness interviews, police told the Dallas Morning News and the Los Angeles Times, investigators “are pursuing the parking space theory.”

“It’s like the Wild West,” McLennan County Sheriff Parnell McNamara told the Dallas Morning News. “These guys become very violent to each other very quickly over nothing.”

Biker gangs Cossacks and Bandidos were “more responsible for the violence” than the three other gangs, police told the Morning News. The Cossacks and Bandidos have been embroiled in an elaborate territorial feud. From the Los Angeles Times:

The purported dispute involving the Bandidos and the Cossacks had its roots in 2013, said former Bandido leader Edward Winterhalder, who now writes books on motorcycle gangs and consults on television shows. The Cossacks club, which was founded in Texas in 1969, offended the Bandidos when it affixed the word “Texas” to the bottom of its colors, a territory-claiming patch also known as the “bottom rocker,” he said.

The Bandidos swiftly warned the Cossacks to remove the label, Winterhalder said, but the Cossacks refused.

Fistfights escalated to worse violence, including an incident in December 2013 when a Bandido leader was accused of stabbing two Cossacks in Abilene, Texas.

On Sunday, Winterhalder said, the Cossacks and their support club, the Scimitars, arrived at the Twin Peaks restaurant prepared for violence.

Waco police apparently knew the groups had planned to meet at the restaurant “about turf concerns and other issues” but that meeting quickly escalated to violence.

“What do gangs fight about?” Waco police spokesman Sgt. W. Patrick Swanton told the Morning News. “Gang stuff. Who’s the baddest gang around. Stupid stuff.”

According to the Waco Tribune-Herald, the Twin Peaks location has decided to permanently close.

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