In 2003, Mr Powell - a cousin of the poet and author Benjamin Zephaniah - died after he was restrained by officers during an incident outside his home.
"When it looks like the sun isn't going to shine anymore, God put a rainbow in the clouds, " sung the 74-year-old, hosted onto the stage by Rastafarian poet Benjamin Zephaniah.
One is Zephaniah Kingsley, a Quaker who ran his northeast Florida plantations in the first half of the 19th century with his African wife, Anna, whom he had bought when she was a teenage slave in Havana.