A leading figure in the Stockholm branch of the American Deserters Committee, Shapiro had recently deserted from Vietnam - he came to Sweden via a Japanese fishing boat and a Soviet ship.
Last week, 39 years on from the original protest, he was back in Stockholm to once again crash an Independence Day party and register his continued dissatisfaction with US foreign policy.
Shapiro's visit to the Swedish capital came just days after the declassification of CIA Documents proving that the agency had established an operational presence in Stockholm with the aim of infiltrating groups likely to influence anti-war sentiment at home.
Did you have any sense at the time that the American Deserters Committee to which you belonged might have been under surveillance by US intelligence?
Absolutely. There was quite a lot of circumstantial evidence that we were being watched. We always suspected that certain deserters and draft resisters were not who they claimed to be.
The fact that the number of staff at the American Embassy swelled considerably at that time was also a telltale sign.
If you imagine an infrared light being held over the world in 1968, Sweden would have emerged as a major intelligence hotspot.
What was it that differentiated Stockholm from other cities in Europe?
Aside from France, Sweden was basically the only European country that would take deserters in. Although we weren't given political asylum, we were permitted to stay on humanitarian grounds.
This, along with people like Olof Palme's sympathetic stance towards Ho Chi Minh, made Sweden very interesting to the American intelligence community.
Also, neutrality created an open political market, which led to horrific CIA asset implications in Stockholm. They wanted to keep an eye on groups like us that could affect domestic opinion in the US, as well as observe how Sweden was reacting with the Soviet Union.
They also wanted to ensure that anti-American tendencies in Sweden did not spread to other Scandinavian countries.
Coming back to the present, why did you return to the scene of your original protest all of 39 years later?
Vietnam was the great tragedy of the time for my generation, which is something that many in Sweden understood. The Vietnam experience is an essential recollection in this time of the Iraq war and I am hoping that thousands will turn out next year for the 40th anniversary of the American Embassy protest.
You have said that last time round you and your colleagues wound up in a prison in central Stockholm and had thousands of Swedish anti-war activists baying for your release. Any similarities this time?
Not really. It was just me for starters. And the Fourth of July celebrations were at the Ambassador's residence rather than the embassy.
I turned up in my best suit and walked past some Swedish police cars and the US secret service guys with the neat haircuts and curly headphones. They directed me towards the registration desk where a woman asked for my ID and my invitation.
I told her that I wasn't invited but had been here before. She then asked me to stand over by a nearby table and a security guy was sent over to talk to me.
He asked me: "Sir, what are you here for?" And I said: "I'm here to protest peacefully." Well, it was like I'd threatened to steal his baby. I could almost detect smoke coming out of his ears.
And that was the end of your protest?
Not quite. Two secret service guys quickly arrived over, grabbed my arms and led me back out onto the street. I was actually quite impressed by how professional they were. To an outsider it might have looked like they were just having a chat with a friend.
I then got ready to start handing out my leaflets about next year's demonstration. The Swedish police tried to stop me but I insisted and eventually they let me get on with it.
One American guy said to me: "You should be shot." It took all his powers of restraint not to punch me in the face. But most of the guests going in were actually really nice about it, saying "good for you" and wishing me luck.
So you'll be back next year?