A police watchdog has submitted a "comprehensive" report on the death of a man in police custody to Scotland's top law officer.

The Police Investigations and Review Commissioner (Pirc) said the supplementary report on the death of Sheku Bayoh would now be considered by Lord Advocate James Wolffe.

Mr Bayoh, 31, died after being restrained by officers responding to a call in Kirkcaldy, Fife, on May 3 last year.

A solicitor for his family said their confidence in the "robustness and impartiality" of Pirc's investigation had been "shattered" and repeated their call for a public inquiry.

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Pirc submitted an interim report to Mr Wolffe's predecessor Frank Mulholland in August of last year.

A spokesman said: "The commissioner has submitted a supplementary report to the Lord Advocate on her independent investigation into the circumstances surrounding the death of Sheku Bayoh and further allegations raised by the family of Sheku Bayoh and their legal representative.

"The commissioner appreciates that this has been a difficult period for the family of Mr Bayoh whilst this complex and wide-ranging investigation has continued.

"A significant part of the work involved the gathering of expert evidence from a range of specialist forensic pathologists to give a greater understanding as to the cause of Mr Bayoh's death.

"During the inquiry, additional lines of investigation emerged which have lengthened the process.

"The commissioner ensured that all of the matters raised were rigorously explored so that the Lord Advocate is presented with a comprehensive report in order that he can make informed decisions on further action.

"The commissioner considered it was important that the quality of the investigation was not compromised by speed."

The spokesman said further inquiries would be carried out at the direction of the Lord Advocate.

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Lawyer Aamer Anwar, speaking on behalf of the Bayoh family, said they remained "determined to fight for justice and the truth".

He said: "This investigation has taken one year and three months to complete.

"Sadly, during this period the Bayoh family's confidence in the robustness and impartiality of Pirc's investigation has been shattered.

"The Bayoh family hope that they can maintain confidence in the new Lord Advocate, James Wolffe QC, to ensure all necessary further enquiries are completed by Crown Office before any conclusion is reached on what happens next. We understand that this process is likely to take some time.

"Whilst the family await the Lord Advocate's decision on the appropriate way to proceed, they believe there is still a need for fundamental reform of Pirc so that no family who loses a loved one through a death in custody is forced to set up a campaign simply to get answers.

"As a result, the Bayoh family maintain their call for a public inquiry to be set up into the death in custody of Sheku Bayoh and into the wider issues raised surrounding police accountability in Scotland."

A Crown Office spokesman said: "The Pirc report will be carefully considered but this is a complex investigation and further work may be required before any decision is made as to whether or not there should be any criminal proceedings.

"The family will continue to be kept informed of any significant developments."

Deputy Chief Constable Iain Livingstone said: "Police Scotland notes that a report by Pirc into the circumstances relating to the death of Sheku Bayoh in Kirkcaldy in May 2015 has been submitted to the Crown Office and Procurator Fiscal Service.

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"Police Scotland, and all the officers involved, have and continue to be committed to working with the Pirc and Crown during the investigative process. As we have previously explained we are unable to comment further while the Crown assesses the independent findings submitted by Pirc.

"Our thoughts remain with Sheku Bayoh's family and friends and in addition we continue to offer support to anyone involved in or affected by the events of May 3 2015."