"This is the worst corruption scandal in modern Los Angeles history," a former federal prosecutor said of the case.
A Minnesota reporter said the protest began peacefully but by Wednesday night tear gas had been used and stores were looted.
"Peter Manfredonia has been found & is in custody" after a nearly weeklong manhunt, officials said Wednesday.
Derek Chauvin had been with the Minneapolis police since 2001. During his career, he was the subject of a dozen police conduct complaints; he was never disciplined.
Floyd, 46, died Monday night after a Minneapolis police officer pinned him by the neck with his knee for more than eight minutes. The president called his death "very sad and tragic."