The inquiry heard on Tuesday that a specific stretch of CCTV recording was absent from the collection gathered by the Royal Ulster Constabulary.
This missing segment covered approximately 22 minutes, a period identified as when the car carrying the suspected bombers likely travelled back into the Republic of Ireland.
A total of 237 CCTV tapes were secured during police investigations, yet no footage showed the vehicle crossing the border into Northern Ireland.
Det Ch Insp Ivan Gault was questioned by legal representatives regarding how these investigations were conducted.
Gault explained that while Aughnacloy station is now considered the probable point where the bombers entered Northern Ireland from the Republic, 52 different locations were initially examined as potential crossing sites.
He noted that the Dungannon Road at Aughnacloy in County Tyrone was unlikely to be the route taken because it housed an RUC station and featured in all three warning calls made before the explosion.
Those warnings, issued around 30 minutes prior to detonation, included the code word Martha Pope used by the Real IRA to claim responsibility for the attack.
The inquiry, which commenced last year with testimony from survivors and bereaved families, aims to establish whether UK state authorities could have prevented the tragedy.
Twenty-nine people, including a woman carrying twins, lost their lives in the bombing of the County Tyrone town on 15 August 1998.
Additional evidence presented included records showing some requests for surveillance video from watchtowers in south Armagh were not submitted until 2005.
Gault confirmed that the timeframe in question coincided with the tracking of phones linked to the bombers moving across the border.
The investigation sought to determine if state authorities had missed opportunities to stop the attack, which occurred near the courthouse in Omagh.