A judicial probe into the assassination of a Roman Catholic lawyer in Northern Ireland reported Friday that it has lost sensitive computer data about the investigation.

The mishap raises fears that witnesses or confidential intelligence sources _ mainly Northern Ireland police officers and British intelligence agents _ could have their personal details compromised. The issue has been a major concern for officers seeking to keep their identities confidential so they do not have to heighten their families’ personal security.

The British government-authorized probe has spent the past three years investigating whether police or intelligence agents were involved in the 1999 killing of Rosemary Nelson, a lawyer who represented the Irish Republican Army and other anti-British clients.

Nelson, 40, died after a bomb attached underneath her car exploded beneath the driver’s seat, blowing off her legs as she drove to pick her children up at school.

The Rosemary Nelson Inquiry announced the loss of the computer data Friday night, a traditional time for seeking to bury bad news. The team said the loss of a disk “containing both personal and protectively marked material” had been discovered 10 days earlier.

“Given the nature of the information, it would not be appropriate to say more about the material involved. The inquiry deeply regrets this serious breach of secure data-handling protocols,” the team’s statement said.

Northern Ireland Secretary Shaun Woodward said police were investigating the loss of the disk and the British government warned the probe team to tighten up its procedures.

Woodward said Britain also had called on the directors of several fact-finding investigations in Northern Ireland to review whether their own sensitive files were adequately protected.

Britain authorized the probes as part of the wider peace process in Northern Ireland, chiefly to boost Catholic support for compromise.

The events under investigation include the 1972 killing of 13 Catholic demonstrators by British troops, the 1996 fatal beating of Catholic civilian Robert Hamill by a Protestant mob, and the 1997 prison assassination of a top Protestant militant, Billy “King Rat” Wright.

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On the Net:

Rosemary Nelson Inquiry statement: http://www.rosemarynelsoninquiry.org/current-key-documents/43