The family of a man who died in police custody said "justice had been denied" after the Crown Prosecution Service (CPS) decided not to press charges.
Kingsley Burrell, 29, from Hockley in Birmingham, was detained under the Mental Health Act in March 2011 and died four days later.
His relatives claimed he was restrained using excessive force.
But on Tuesday the CPS announced there was insufficient evidence to secure a conviction.
At a news conference held on Friday, Mr Burrell's sister, Kadisha Burrell, said she was determined to continue campaigning for a criminal case to be brought against West Midlands Police.
"Not to get justice is unbearable, for the family as well as the community."
"It doesn't matter how long it takes, we will get justice eventually."
In a statement, the CPS said: "Officers and medical staff were presented with an ongoing and difficult set of circumstances.
"We understand it is not the decision that Mr Burrell's family will necessarily have wanted and we have offered to meet them to discuss this matter."
A date for an inquest into the death of Mr Burrell has not yet been set.