The Rainbow Warrior was on its way to protest French nuclear testing on a Pacific atoll, when Jean-Luc Kister used a limpet bomb to sink the vessel in July 1985.
A Portuguese photographer named Fernando Pereira was killed in the blast, and Kister says the death has weighed heavily on his conscious ever since.
“Thirty years after the event, now that emotions have subsided and also with the distance I now have from my professional life, I thought it was the right time for me to express both my deepest regret and my apologies,” the Daily Mail quoted him as saying.
“I have the blood of an innocent man on my conscience, and that weighs on me. We are not cold-blooded killers. My conscience led me to apologise and explain myself.”
Kister was ordered to sink the ship by the French government, but his name was subsequently leaked to the media shortly after the attack. He added that he considers his unmasking to be an act of high treason.