In the hopes of getting a bit more traffic to this forum and putting the relevant background information out there, here is the PDF of the full list of officiating quintets for EURO 2012. Each group has a stand-by AR who will only be called upon if one AR has to drop through injury or other unforeseen reason: http://www.uefa.com/MultimediaFiles/Download/competitions/General/01/77/43/22/1774322_DOWNLOAD.pdf