Following a day of peaceful demonstration over the death of Freddie Gray, who died of a broken neck while in police custody last weekend, 12 of an estimated 1,200 protesters were arrested in Baltimore Saturday night after a breakaway group smashed windows, damaged cars and battled with police, The New York Times reports.

Chanting “all night, all day, we’re gonna fight for Freddie Gray,” hundreds marched through the city’s streets yesterday, holding signs and blocking traffic before converging at City Hall. From there, a group of as many as 100 split off toward Camden Yards where the destruction began just before sundown.

As night fell, the number of protesters on the streets dwindled, but a “splinter group” of those that remained trashed nearby businesses, smashed parked cars and threw objects at police, injuring at least five officers, according to Time.

Condemning the actions of the destructive faction as “unacceptable” at a press conference Saturday night, Baltimore Mayor Stephanie Rawlings-Blake noted 95 percent of demonstrators were peaceful but “a small group of agitators intervened and turned what was otherwise a peaceful demonstration into a violent protest.”

At that same press conference, Freddie Gray’s twin sister Fredericka urged non-violence, saying, “My family wants to say, ‘Can y’all please, please stop the violence? Freddie Gray would not want this.’ Freddie’s father and mother do not want any violence. Violence does not get justice.”

On Friday, Police Commissioner Anthony Batts admitted that officers had failed “multiple times” to get medical attention for Gray, who died of a severed spinal cord after being arrested on Sunday. According to Batts, investigators are exploring whether Gray was injured during a so-called “rough ride,” an unofficial practice where officers drive erratically in order to harm handcuffed but unbuckled suspects.

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