St Louis - St Louis police made several arrests and one officer was injured on Sunday night after an afternoon of nonviolent protest over the acquittal of a white former police officer charged in the shooting death of a black man gave way to broken windows and a police response of several hundred officers in full riot gear.Following the same pattern as the previous two days, Sunday's protests began as marches of hundreds of people chanting in opposition to the verdict released on Friday. But after organisers declared the demonstration a success and urged participants to head home, several dozen remained and grew increasingly agitated as the evening wore on.By the time buses carrying hundreds of officers arrived, windows were broken at several businesses, plants were pulled from decorative downtown planters and police said they were sprayed with an unknown chemical.At least seven people were taken into custody.Heading into a third night of protests, organisers said they were frustrated that a few people who have caused trouble at night could make it harder to spread their nonviolent message.State Representative Bruce Franks, who has participated in the protests, said those who are violent and vandalising "are not protesters" but a group separate from those marching in organised demonstrations.Protesters object to the not-guilty verdict released on Friday for Jason Stockley, who had been charged with first-degree murder in the killing of Anthony Lamar Smith in 2011.Broader messagesAuthorities closed off several blocks around the police headquarters on Sunday afternoon in anticipation of the demonstration, which followed two days of nonviolent marches that devolved after sunset when small groups turned violent on Friday and Saturday nights.Protesters and organisers say the violence and vandalism by a few people threatens to detract from broader messages of racial equity.Protest organiser Anthony Bell during demonstrations on Sunday said change is made through peaceful protests, such as those led by Dr Martin Luther King jnr. But Bell said he understands the anger that sometimes leads to violence and property damage."I do not say the demonstrators are wrong, but I believe peaceful demonstrations are the best," he said.The recent St Louis protests have followed a pattern borne out of months of angry and sometimes violent protests after the 2014 killing of Michael Brown in nearby Ferguson: The majority of demonstrators, though angry, are law-abiding. But as the night wears on, a subsection emerges, a different crowd more willing to confront police, sometimes to the point of a violent interaction.