The mother of a vulnerable man who died after being restrained by police has spoken of her devastation after learning that officers will face no criminal charges.

The police watchdog passed a file to the Crown Prosecution Service (CPS) in March 2016 concerning two Bedfordshire police constables, three sergeants and a member of police staff, suggesting they may have committed crimes related to the death of Leon Briggs in 2013.

Prosecutors said in January that no action would be taken against one of the officers, and they have now confirmed that the other five people will also face no charges.

Margaret Briggs said: “I am devastated that after almost five long years I am no closer to finding out what happened to Leon or to getting some accountability for his death.”

In a statement released by her lawyers, she said: “My son was struggling with his mental health. That struggle should not have resulted in his death at the hands of Bedfordshire police.

“My one hope is that the inquest into Leon’s death can start as soon as possible. I am desperate for some answers and hopefully, in time, some closure.”

Briggs died on 4 November 2013. He had been detained in Luton under the Mental Health Act after people expressed concern about his welfare.

The Independent Police Complaints Commission, since renamed the Independent Office for Police Conduct, investigated and asked prosecutors to consider whether or not manslaughter and misconduct charges should be brought.

A CPS spokeswoman said it would not be taking any further action in the case, adding: “We have now examined the evidence against the remaining individuals and the force itself, and concluded our test for bringing a prosecution is not met.”

Margaret Briggs’ lawyer, Jocelyn Cockburn, of the firm Hodge Jones and Allen, said: “No mother should have to wait five years to find out what led to the death of her son. In order for her to have had any confidence in the investigation, it needed to be open and transparent, which this was not.

“However, that is exactly what the inquest process must achieve. I hope that the coroner will now resume the inquest into Leon’s death, allowing a public examination of the facts.”

Deborah Coles, the executive director of the charity Inquest, said: “Excessive delays and negative prosecuting decisions are sadly all too familiar when it comes to deaths following the use of force by police officers.

“There is a systemic reluctance on the part of the CPS to allow a judge and jury to determine criminality in these cases, which begs questions as to whether the rule of law applies to police officers. Another family now look to the inquest to provide a semblance of accountability.”

An inquest into Briggs’ death was opened and adjourned in January 2014 at Hertfordshire coroner’s office.