The Police Investigations and Review Commission (PIRC), which will investigate serious wrongdoings in Scotland's new single force, is facing criticism over its recruitment process after 13 out of a total of 20 appointments (65%) were given to candidates with a policing background.
It follows a recent Home Affairs Select Committee report into the body's English equivalent, the Independent Police Complaints Commission (IPCC), which recommended that just 20% of investigators should have links to the police.
The PIRC claims it has selected the best people, but leading human rights lawyer John Scott, QC, claims the balance is wrong and there is a risk of investigators subconsciously favouring the police.
Mr Scott said: "You need the right balance of staff – enough former police officers to allow an understanding of how things work, but also people who have not been close to it to help balance it out.
"The current ratio isn't right and will certainly do nothing to bolster the confidence of the public. That's not a dig at the integrity of those already involved, but the fact is that the PIRC needs the right balance of people, and that doesn't appear to be the case."
Mr Scott added that the commission should have taken on board evidence from the select committee to avoid the perception of police investigating themselves.
The PIRC investigations team, which is being led by former Strathclyde CID head John Mitchell, will be responsible for investigating criminal and serious misconduct allegations against the police, as well as deaths with police involvement.
Labour MSP Lewis Macdonald said: "It is essential the PIRC is independent and that the work they do is not compromised by a public perception of an old pals act. Given the number of ex-police on the team, Mr Mitchell will have to work even harder to prove that his investigations will be carried out without fear or favour."
However, the Scottish Conservatives argued the recruitment of so many police officers was appropriate.
Chief whip John Lamont said: "What's essential is those investigating problems in the force have a very definite experience of what they are looking at. We believe the current ratio appears to be appropriate.
"It would be more of a concern if policing experience was absent from the panel."
A PIRC spokeswoman said staff were selected for their skills in areas such as family liaison, specialist intelligence techniques and crime-scene management.
She added: "We have selected what we believe to be the best people for the job.
"Our recruitment policy is clear, the application and interview process followed is competency-based, and all candidates are required to evidence their relevant experience in the application form. For those invited for interview, this is further tested and the results discussed by a panel that included people with no police background.
"The quality of the investigations we undertake is how we will provide assurance to the public of the independence of the organisation."