Family members and friends of people who died while in police custody held a march in central London to demand justice for their loved ones.
About 300 protesters took part in the annual procession by the United Families and Friends Campaign.
The demonstrators marched from Trafalgar Square to Downing Street.
Ajibola Lewis, whose son died after being restrained by officers in August 2010, said "police have to be held accountable for their actions".
Ms Lewis' son, Olaseni Lewis, died days after he was restrained three times - first by hospital staff and then by 11 police officers - for 45 minutes in a south-east London psychiatric hospital.
She said she was still waiting for an inquest to be held, four years on.
"This is happening all the time and it's not just black people, it's Asian and white, men and women," she said.
"The police have to be held accountable for their actions - if you kill somebody you should be prosecuted."
She also called on the Independent Police Complaints Commission (IPCC) to "get a move on" with its investigation.
"You have to fight every battle every step of the way is a fight," she added.
"You just feel you are on your own."
In a statement, the IPCC said: "The investigation, examining the circumstances surrounding police contact with Mr Lewis, together with any action taken or decisions made by police officers, is ongoing."
The protesters carried placards, reading "No Justice No Peace" on the route through Whitehall.
Deborah Coles, director of Inquest - which campaigns for people bereaved by a death in custody, said the procession was an "important but poignant" day.
"Many families feel betrayed by a system that has let them down," she said.
"The same issues repeat themselves time and again despite the empty platitudes from Government ministers that lessons will be learned."