The Independent Police Complaints Commission has apologised for the length of time taken to investigate the death of Leon Briggs.
The father-of-two died after being held in custody at Luton Police Station on November 4 2013, under section 136 of the Mental Health Act.
Despite a number of false dawns the IPCC has still not published its findings on the case almost two years on.
Six officers remain under investigation and are currently suspended on full pay.
In a letter to police and crime commissioner Olly Martins, IPCC commissioner Mary Cunneen said: “Although it is necessary in the public interest to ensure that our investigation and the report on it is thorough, I would like nonetheless to apologise to those affected, in particular the family of Mr Briggs, but also Bedfordshire Police and the officers under investigation, Luton Council and the wider community that our investigation has taken longer than I would have hoped.
“I would also like to provide assurances that we are committed to completing the investigation as quickly and thoroughly as possible.
“This is a complex investigation, which we would expect to take some considerable time to complete, and some of the delays are due to circumstance beyond the IPCC’s control.
“However, the investigation has taken longer than I would have liked, or envisaged at the outset.”
Ms Cunneen told the PCC that the police watchdog expects to conclude the probe very soon, but does not indicate when a final report is expected.
She wrote: “We are currently following up a few final enquiries and clarifying some information received so that we have all the relevant evidence needed to complete the report.
“I can assure you that the investigation is of the highest priority within the IPCC.
“The progress of the investigation has been reviewed by the chair and chief executive and we have brought in additional resources to speed up the completion of the investigation and the report.”
On the delays taken to complete the report, Ms Cunneen said that the investigation had been held up by the ‘considerable amount of time gathering evidence’.
She added that the IPCC had sought the input of medical and mental health experts, one of whom it spent 10 months going back and forth with.
Ms Cunneen wrote: “While this is a long period of time, it must be borne in mind that experts have other professional demands on their time, and that the full extent of enquiries will sometimes only become apparent once reports and other expert evidence have been received and considered.”
This process concluded last month, when an East of England Ambulance Service internal investigation report was also received by the IPCC.
PCC Olly Martins, who previously slammed the IPCC for its “expensive and slow” investigation, welcomed the letter.
He said: “Naturally, I want to see a comprehensive investigation undertaken, and accuracy should never be sacrificed for speed, but I also think that the family of Mr Briggs rightly feel that it is time that they had some answers.
“It is also important the plight of the suspended officers and staff and their families is not overlooked.
“They too are waiting for answers.
“In addition, I think that the taxpayer has a right to expect that the £24,000 per month cost associated with the suspension of officers and staff while they await the report, should be kept to a minimum.
“This is money that should be used for policing, whatever the findings of the IPCC, and while there must be accountability if there is any culpability, we need to know if this is the case or not.
I think that patience is running out while people wait for the outcome of this investigation.”