The defence team at the Omagh bomb trial has claimed that items were added to evidence before it was taken to be examined by DNA specialists.
Twenty-nine people died in the Omagh bombing
The judge said that it appeared that black tape had been deliberately placed on the lid of a bomb timer.
The timer power unit from a car bomb attack in Lisburn was taken to Birmingham to be examined at a forensic laboratory there.
Sean Hoey, 37, from Jonesborough, denies a total of 58 charges.
The prosecution are trying to link Sean Hoey to the Lisburn attack and other bombings through DNA evidence.
On photographs taken in Birmingham, black tape is clearly on the lid of the timer - but a forensic scientist told the court that the tape was not there when he examined the timer months earlier at a lab in Northern Ireland.
Defence QC Orlando Pownall said he would be arguing that an individual or individuals had put the tape in the evidence bag.
The issue has been raised several times now during the trial and on Tuesday the judge Mr Justice Weir described the sudden appearance of the tape as "Houdini-like".
Details of a number of the other bomb and mortar attacks Sean Hoey is accused of were given.
In several cases the court was told that the devices were capable of killing people.
Among the charges Mr Hoey faces is the murder of 29 people in the Omagh bomb attack in August 1998.
The trial continues.