The family of a Catholic man beaten to death by a loyalist mob have spoken of their anger after case files were lost in the post.
Sensitive information on the murder of Robert Hamill in Portadown 18 years ago went missing earlier this month.
Files on two other judge-led inquiries, including the police shooting of Mark Duggan, are also missing, the Ministry of Justice (MoJ) said.
The blunder has sparked a major security alert with police officers warned their identities could be leaked.
The marksman who killed Mr Duggan in north London in 2011, sparking England-wide riots, has never been made public. Relatives of Mr Hamill have requested an urgent meeting with officials. They want to know if previously unpublished material is contained in the lost files.
"We are at a loss to understand why any material relating to the Robert Hamill inquiry should have been posted or sent at this particular time, given the fact that the inquiry report itself was completed in February 2011," the family said.
Officials realised two discs containing documents about the Duggan, Hamill and Azelle Rodney inquiries were lost earlier this month.
In a statement the MoJ said police have taken "necessary steps" to ensure the protection of any officers whose information could be disclosed.
Meanwhile, the Government has launched an investigation into the security breach of its guidelines and said disciplinary action will be taken if appropriate.
All three men died in controversial circumstances, resulting in judge-led inquiries.
Mr Hamill, a 25-year-old Catholic, was attacked and beaten by loyalists in Portadown in 1997.
Mr Duggan's shooting in north London in 2011 sparked the biggest riots in modern English history.
Meanwhile, Mr Rodney (24) was shot six times while travelling in a car that was stopped by police in Edgware, north London, in April 2005.