Commander Dominic Murphy, then a Hertfordshire officer and bomb scene examiner, drove to London immediately after the attacks on 7 July 2005, without waiting for official deployment.
He was deeply impressed by the professionalism, commitment, and compassion of the counter-terrorism officers he met at the scene, he said.
This experience inspired him to dedicate his entire career to counter-terrorism, remaining in London.
Mr Murphy, who specialised in body recovery, has since been deployed internationally to investigate other atrocities involving British victims or interests.