Senior Lebanese intelligence official Wissam al-Hassan, who led the investigation that implicated Syria and Hezbollah in the killing of former prime minister Rafik al-Hariri, was killed in the Beirut explosion on Friday, a Lebanese official said.
"I can just say that it is true, he is dead," the official, who worked with al-Hassan, told Reuters.
Al-Hassan was also the brain behind uncovering a recent bomb plot that led to the arrest of a Lebanese politician allied to President Bashar al-Assad.
Al-Hassan was no ordinary officer. He was a close aide to Hariri, a Sunni Muslim who was killed in a 2005 bomb attack.
He led the Hariri investigation and uncovered evidence that implicated Syria and Lebanon's pro-Iranian Shi'ite Muslim group in the killing.
Hariri supporters accused Syria and then Hezbollah of killing him - a charge they both deny. An international tribunal accused several Hezbollah members of involvement in the murder.