His aircraft received several catastrophic hits from the anti-aircraft guns during his bombing runs and it crashed, killing Trigg and his crew, so the only witnesses to his high courage were the U-boat crew members..
The U-boat sank but its crew were rescued by the British and the captain reported the incident, recommending Trigg be decorated for his bravery. The Victoria Cross was awarded posthumously
External source: http://members.ozemail.com.au/~vcweb/winners/nz_winners/trigg.htm