LONDON — A man who used a narwhal tusk to fight off a knife-wielding suspect during a terror attack on London Bridge last month has finally spoken out about the incident, saying he feels "deep hurt" because he was unable to save the two victims.

The attack on Nov. 29 saw Jack Merritt, 25, and Saskia Jones, 23, fatally stabbed by Usman Khan, 28, who had targeted an event for a prisoner rehabilitation program in Fishmongers' Hall, a historic building adjacent to London Bridge.

Darryn Frost, 38, was attending the event and among the bystanders who jumped into action when Khan struck.

"When we heard the noise from the floor below, a few of us rushed to the scene," the South African-born civil servant who has lived in Britain for 14 years, told the U.K.'s Press Association news agency Saturday.

"I took a narwhal tusk from the wall and used it to defend myself and others from the attacker," added Frost, whose identity has remained a mystery until now.

Video posted to social media from eyewitnesses immediately after the incident showed Frost and at least three other men chasing after Khan on London Bridge and pinning him to the ground.

"He had knives in both hands and, upon seeing me with the narwhal tusk, pointed at his midriff," said Frost, who works for the U.K.'s Ministry of Justice. "He turned and spoke to me, then indicated he had an explosive device around his waist.

"At this point, the man next to me threw his chair at the attacker, who then started running toward him with knives raised above his head."

After giving the tusk to another unarmed bystander Frost said he ran to find another one in the building to defend himself.

The first tusk ended up shattered across the floor. Frost used the second one to pursue Khan onto the bridge while people began fleeing the building.

As bystanders finally managed to restrain the attacker, Frost said he remained focused on trying to hold his wrists down so he couldn't stab anyone with the knives taped to his hands or set off the explosive vest, which police later determined to be a fake.

Police eventually shot and killed Khan, who was previously convicted of terrorism charges but released from prison last year.

Frost said he was coming forward with his story hoping to raise money for the victims' families and to urge people to unite against terrorism.

"I hope that the part I played in these terrible events can be used for good," he said.

Offering condolences to the victims' families, Frost said: "In reading about their lives and work I am convinced they represent all that is good in the world, and I will always feel the deep hurt of not being able to save them."

He urged people to support his project, Extinguish Hate, and donate to the victims' families fundraising websites.