Discs containing information about the fatal police shootings of Mark Duggan and Azelle Rodney have gone 'missing in the post', the Ministry of Justice has admitted.
The sensitive material, which also includes details of the inquest into the death of Robert Hamill, who was beaten to death in Northern Ireland in 1997, disappeared three weeks ago.
One member of staff has been suspended since the loss of the two discs, and the government is said to be taking the loss "extremely seriously".
The discs contain information on the investigations into the fatal shootings of Mr Duggan, in 2011, and Mr Rodney, in 2005, by police in London. A police marksman is due to face trial for Mr Rodney's murder later this year.
Mr Duggan's death sparked riots across the UK, and the data is believed to include details given by a number of firearms officers.
It is not clear whether the officers' names - or names of witnesses - were contained in the lost files. But the MoJ said police forces had been warned about the error to enable them to take "any steps necessary to ensure the protection of officers".
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"The government takes information security extremely seriously, and this incident is a breach of the arrangements that should be in place," the government said in a statement.
"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."
It said “intensive searches” had been carried out with the help of police - but had failed to recover the missing discs.
It also said that the Rodney, Hamill and Duggan families had been informed and confirmed that the investigation "could lead to disciplinary action".
A spokeswoman for the Information Commissioner's Office said they had been made aware of a "possible data breach", the BBC reported.
“We will be making enquiries into the circumstances of the alleged breach before deciding what action, if any, needs to be taken.”Reuse content