Retired Detective Tom Needham bravely jumped into more than 10 feet of water to pull the 22 year old killer from his car.
Gallagher had driven off a pier near Donegal Town as he went on the run after killing mother and daughter Anne and Annie Gillespie in the grounds of Sligo General Hospital on September 18th, 1988.
He had fixed himself to the steering wheel of the car with handcuffs he had brought but Tom managed to get a cutters and drag Gallagher to safety.
Amazingly the former detective, who retired 11 years ago, says he thinks Gallagher was under-water for up to 20 minutes.
He told Donegal Daily “Again the emergency services got there and stuff, I would say it was up to 20 minutes.
“I think there may have been a pocket of air in the car which helped him to survive.
“When I got him out of the water, I squeezed his stomach very hard and he started to come around a bit. He didn’t say anything because he wasn’t in a state to speak,” said Mr Needham.
Looking back to the shocking events almost 25 years ago, Tom, who was then in his 40s, said he was only doing his duty.
And he says he would do the same thing again.
“The thinking that any Garda has is that it is part of our training. Our thought is always on the preservation of life and that’s my thought today despite all that has happened,” he said.
Tom said he never thought Gallagher was insane because he drove his car and tried to get back to his home in Lifford but was caught.
Although he may now be planning a bid for freedom from the Central Mental Hospital where he handed himself in two weeks ago, Tom says Gallagher will always have a life sentence hanging over him.
“Maybe it has started to play on his mind now. If it had not stuck there may be a few more on his list.
“My job was to save his life. He has to live with the rest of his life with his actions and it plays on his mind every day for the rest of his life.
“It’s a sentence even though he might be a free man he has to live with it. It’s a life sentence for everyone involved,” he said.
Despite his heroic actions in saving a life, Tom revealed he has never been recognised for his actions.