"The shooting occurred in the Israeli men's Olympic team apartments, right next door to our New Zealand team accommodation.
A shootout and grenade explosion occurred... and hardly anyone survived.
"I eventually got back to my room and, as the day unfolded, was witness to shooters on the roofs of buildings all around me.
"I saw the German Vice Chancellor, Willy Brandt, negotiating with Palestinian guerrillas who had broken in and stormed the Israeli quarter."
Eleven Israeli Olympic team members and a German police officer were taken hostage, tortured and eventually killed by the Palestinian terrorist group Black September.
"I witnessed the eventual departure of the guerrillas by helicopter from the Olympic village green.
"Of course, a shootout and grenade explosion occurred at the airport, where the guerrillas were hoping to transfer to a waiting plane, and hardly anyone survived."
Of the hostages, only three survived, while five of the eight Black September members were killed by police.
"It was a very sobering experience and one that lives on for those of us who were there."
Forty-five years on, Gavin has other standout memories from his years as a young leading sportsman.
Before the Olympics, he ran for New Zealand in two international cross-country championships, one in Scotland during 1969 and a 1971 event in Spain.
In the same year, he won the Belgian cross-country title, defeating the Olympic steeplechase champion, becoming world 10,000 metre record holder.
The 1972 Olympic Games was his last major sporting challenge however, his performance was affected by a then-undiagnosed congenital back problem.
"The problem emerged when the New Zealand athletics team arrived in Scandinavia for three weeks of pre-Games competition.
"Thinking it was a slipped disc, I was put under the care of an osteopath travelling with the American team, who were taking part in the same athletic meetings as us.
"I did not progress beyond the heats in both the 5000 and 10,000 metres track events.
"It was only discovered after my return to New Zealand that the problem was a couple of incomplete lumbar vertebrae."
Unfortunately, it spelled the end of his career as a top athlete.
Pushing the experiences to the back of his mind, Gavin focused on qualifying as a graphic designer, before going on to work in the advertising and newspaper industries.
Stints as a retailer and shopping centre manager followed, with the father of three eventually transitioning to property management and development.
"I managed property teams at two of the country's largest local authorities, but 10 years ago I decided to work for myself here in Kapiti.
"I took on management of mostly commercial and development property for a small number of clients and for five years, commuted to New Plymouth from Kapiti each week.
"On completion of my contract there, I was looking for some community activity to become involved in."
Naturally, he searched for something where his business or sporting background could help.
In 2008, Gavin became involved with Special Olympics in Kapiti, where he now is chairman.
This year, Gavin will again find himself among the atmosphere of the games, when his team competes at November's Special Olympics National Summer Games in Wellington.
Running on a four year cycle, the games includes basketball, ten pin bowling, football, swimming and golf.
According to Gavin, Kapiti has a team of 42 athletes and support volunteers registered for the event.
To get there, the club has been trying to raise $31,500 needed to cover registration, student accommodation and new uniform costs.
Thanks to local charitable institutions and individuals, the group now has $9000 to go.
"A big thank you to everyone who supports our Special Olympics athletes.
"We are very grateful for any monetary contributions, or products and services that can be prizes in a raffle or auctioned on a fundraising night."
Gavin, a former Kapiti College student, admitted that at 70 years old he should probably be easing back on his work commitments. But he is not ready to let go of the excitement of competitive sport, or the people he helps.
"Working with athletes who suffer from varying degrees of intellectual disability is challenging, but also very rewarding.
"Being an Olympian, it felt like there was a good synergy."