Information relating to three judge-led inquiries - including the murder of Robert Hamill - have gone missing in the post, the Ministry of Justice (MOJ) has confirmed.
Two discs containing documents about the Mark Duggan, Azelle Rodney and Robert Hamill inquiries have been lost since earlier this month.
In a statement, the MOJ said it has launched an investigation into the security breach, which it said is against its guidelines.
Robert Hamill, a 25-year-old Catholic who lived in Lurgan, was beaten by a loyalist mob in Portadown in April 1997.
The father-of-three suffered serious head injuries and died 11 days after the attack.
The Ministry of Justice said: “The government is investigating an information loss, relating to 3 independent judge-led inquiries.
“The government takes information security extremely seriously, and this incident is a breach of the arrangements that should be in place.
“The independent inquiries in question are the Azelle Rodney Inquiry, the Robert Hamill Inquiry and the Mark Duggan Inquest. All 3 have completed their work, although the Hamill Inquiry has yet to publish its report.
“At this stage there is no evidence to indicate that the information loss arose from malicious intent. Nevertheless, it is essential to take the most precautionary view and to take all necessary steps to safeguard the interests of anyone whose information could be disclosed.
“Police and other agencies have undertaken their own risk assessment, and have identified and taken any steps necessary to ensure the protection of officers.
“The Rodney, Hamill and Duggan families and the 3 judges who conducted the inquiries and inquest have been informed. So too has the Information Commissioner’s Office.
“Government officials became aware on 8 January that 2 discs containing documents relating to these inquiries were missing, having been dispatched by post. Immediate steps were taken, including intensive searches to locate the discs. These searches continue, with police assistance. The discs have not, as yet, been found.
“Treasury Solicitor’s lawyers were commissioned to undertake a review of all the documents in question, to identify any confidential or sensitive information relating to individuals or agencies and enable any risks to be assessed. Individuals will be contacted, where appropriate, to inform them of any personal information relating to them.
“As well as safeguarding individuals’ interests, the government has undertaken urgent investigations into how this incident was able to happen, and further investigations continue in relation to both the conduct of individuals and the organisational safeguards against information security breaches of this kind. A member of staff has been suspended to facilitate the investigation. Once concluded disciplinary action will be taken if appropriate.
“As part of this, an independent review has been commissioned to look at all the circumstances of this loss and identify lessons learned. The review will report jointly to the Ministry of Justice and Cabinet Office to identify any wider lessons to be learned and shared that pertain to inquiries and other independent processes.
“The government will continue to work closely with the Information Commissioner, and will welcome any investigation that his office may wish to undertake.
“A copy has been placed in the libraries of both Houses.”