A car belonging to one of the suspects in the raid that led to Det Gda Adrian Donohoe being shot dead drove by the scene less than eight hours before the incident, the Central Criminal Court heard on Friday.
Det Garda Gareth Kenna said a face appeared to be visible through the open front passenger window as the BMW 5-Series passed by at 1.46pm.
Seconds later the vehicle could be seen on CCTV with the same passenger window closed, he added.
The robbery, at Lordship Credit Union in Bellurgan, Co Louth, on January 25, 2013, took place at around 9.30pm that night.
Aaron Brady, 28, from New Road, Crossmaglen, Co Armagh, has pleaded not guilty to the capital murder of 41-year-old Det Gda Donohoe.
He has also pleaded not guilty to a charge of robbing approximately €7,000 in cash and assorted cheques on the same date and at the same location.
Det Gda Kenna also described a man identified as the suspect for the robbery getting out of his car at Bellurgan Service Station and buying two bottles of water minutes before his vehicle drove by Lordship Credit Union.
The jury has been viewing CCTV footage from Co Louth in the days leading up to the raid.
The trial continues.
