Pounding rain and tornado watches didn't deter hundreds of protesters Monday outside Ferguson police headquarters, where they stayed for almost four hours to mark how long 18-year-old Michael Brown's body was left in a local street after he was fatally shot by police.

Nearly 20 people were arrested — including scholar and civil rights activist Cornel West — and some protesters used a bullhorn to read the names of people killed by police nationwide. The rally was led by clergy members on a third straight day of protests in the St. Louis suburb where Brown was unarmed when he was fatally shot on Aug. 9.

Protests have been common since Brown, who was black, was killed by a white police officer. But tensions escalated last week when a white police officer in nearby St. Louis shot and killed another black 18-year-old, Vonderrit Myers Jr., who police say shot at officers before he was killed.

"My faith compels me to be here," said Bishop Wayne Smith of the Episcopal Diocese of Missouri. "I want to show solidarity, and call attention to the structural racism of St. Louis."

Protesters were met by about 40 officers in riot gear. Several clergy members approached individual officers and asked them to "repent" for Brown's killing and other acts of violence. Some officers engaged the protesters, while others ignored the efforts.

"My heart feels that this has been going on too long," Ferguson officer Ray Nabzdyk told the clergy. "We all stand in fault because we didn't address this."

St. Louis County Police spokesman Shawn McGuire said about 13 people were arrested at police headquarters on charges of peace disturbance. Six others were later arrested for failing to disperse after blocking a street.

Organizers had promised civil disobedience Monday. Hundreds of people marched to Saint Louis University earlier in the day, though no arrests were made, and about 100 protesters marched into St. Louis City Hall blowing whistles and chanting, "Hands up. Don't Shoot," a common protest mantra since Brown was killed. A small number of police officers watched passively as protesters made their way into City Hall, and an aide to Mayor Francis Slay led some of them upstairs after they asked to see the mayor.

The planned demonstrations began Friday, with protesters marching to the St. Louis County prosecutor's office and renewing calls for charges against Darren Wilson, the officer who shot Brown. A grand jury is reviewing the case, and the U.S. Justice Department is conducting a civil rights investigation.

Events over the weekend were mostly peaceful, though officers arrested 17 protesters and used pepper spray Sunday in a St. Louis neighborhood where about 200 people gathered not far from where Myers was killed. The protesters, some wearing masks, marched toward a QuikTrip convenience store and tried to force open its doors, according to police.

Myers, who died Wednesday, was among three black males killed by police in the St. Louis area since Brown's death. Police said the officer fired 17 rounds after Myers opened fire. Myers' parents say he was unarmed, and many speakers at a weekend rally echoed those doubts and raised concerns about racial profiling