In a review of two years of work by the Northern Ireland Forensic Science Agency, "errors" were uncovered in more than a third of cases, the Omagh bomb trial heard yesterday.
Giving evidence at the Belfast Crown Court trial of Seán Hoey (37), the acting operations director at the agency, Samuel James Speers, revealed that during a review of 1,200 cases carried out between November 2001 and October 2003, errors were uncovered in 455 cases.
Although the senior forensic scientist, with 18 years experience, added they were mostly "administrative errors", he conceded to trial judge Mr Justice Weir that immaterial who made the mistakes, "errors still resulted".
The review was carried out by consultancy firm Helm, during a time when the UK Accreditation Service had suspended the FSNI's accreditation.
However, Mr Speers claimed the consultancy firm had identified that many of the errors had originated from outside his agency. Mr Speers, who said he wanted to "give a fuller description of what those errors were", will return to the witness box today to continue his cross examination from defence lawyer Kieran Vaughan.
Earlier the trial also heard there is worldwide "confusion" over low copy number DNA, the system whereby evidence may be extracted from very small amounts of DNA.
LCN evidence is one of the main planks in the prosecution case against Mr Hoey, who denies 58 terror charges including the murders of the 29 victims of the August 1998 Omagh bomb atrocity.
Its evidential value has come under scrutiny throughout the trial and yesterday's admission came from forensic expert Dr Peter Gill during further exchanges with Mr Justice Weir.
Dr Gill said the LCN technique was "still developing".