The acquittal of three activists yesterday on charges of vandalising the Waihopai spy base near Blenheim does not set a legal precedent, but other defendants may consider using the same "greater good" defence, a criminal law expert says.

Adrian Leason, Peter Murnane and Sam Land admitted they broke into Waihopai and slashed an inflatable plastic dome covering a satellite dish, but pleaded not guilty to wilful damage and burglary charges because they believed their actions were lawful.

Law Society criminal law sub-committee convenor Jonathan Krebs told Radio New Zealand he had never heard of a defence referring to a greater good before.

"[The Waihopai defendants] claimed that they honestly believed that they had the right to do so because they needed to, for certain honestly-held beliefs."

No precedent was created by their acquittal, because precedent was only set by judicial decisions on matters of law, not jury decisions on facts, he said.

"I can imagine, as often happens when a defence is raised and receives such widespread publicity and discussion, that others might be interested in at least considering advancing it but...there's actually no binding effect from the decision of the jury."

Mr Krebs said the "claim of right" defence used by the trio was enshrined in statute law, but usually used in property cases.

An example of its regular use would be as a defence when stolen property was unwittingly purchased, with the purchaser believing the seller owned and had a claim of right to the property, Mr Krebs said.

A jury in Wellington District Court yesterday took only two hours to find the trio not guilty after a trial lasting eight days.

The Waihopai base is operated by the Government Communications Security Bureau (GCSB), which has not yet commented on the verdict.

Murnane said the trio weren't sure their line of defence would succeed, but they knew what they had done "was right" because it was done for the greater good.

"That brought a claim of right and we knew we had a right to do that because we were saving people from much greater evil than the mere cutting of a bit of plastic."

The verdict quickly drew reaction from the blogosphere, with Whaleoil's Cameron Slater writing: "I've now got a nice defense because I have a belief in a higher law, a law for protecting people from paedos, rapists, wife bashers and thugs."

Slater is currently facing charges related to posts he wrote that gave clues to the identities of people with name suppression who appeared before the courts.

And David Farrar, who runs popular right-wing Kiwiblog, said: "I think the verdict reflects that many NZers do not like spy stations, regardless of the actual applicable law.

"What will be interesting is if this sets out a spate of attacks on properties by protesters, who will hope for a similar outcome.

"As for Waihopai, they may need to invest in some extra guards with tasers!"

Scoop's Gordon Campbell said the decision to acquit was likely to have been based on social grounds as well as on points of law.

"The jury may well have sensibly concluded that no useful social purpose would be served by convicting and imprisoning these three men for the damage they had done to public property, given their sincerely held beliefs," he wrote.

"Any future jury pool will be more likely to be aware of the argument of moral necessity advanced by the Waihopai Three, just as any future protester thinking of doing damage to public property will now be more aware of this defence, and its potential for success."

Radio announcer Pat Brittenden said the protesters were easily found not guilty as they were "passionate in their belief" and didn't believe they were committing a crime.

"Saving human lives is the greater good over costing the country $1 million and temporarily incapacitating the base.

"The big question is now that this case has set a precedence, who will use it for what 'cause' next?"

On Twitter, Aucklander TheHeindog summed up one view: "The Waihopai spy base case is a great advertisement for the uselessness of the jury system."

Meanwhile, Green MP Keith Locke said yesterday the acquittal was a victory for the peace movement, which has campaigned for the closure of the base.

"I hope that the not guilty verdict will help break down the blanket of secrecy that successive governments have imposed around the operations of the base, and its true purpose," he said.

The Christchurch-based Anti-Bases Campaign went further, calling for prosecution of the base operators for crimes against humanity.

Spokesman Murray Horton said the "Domebusters" had believed they had the law on their side and were proud of what they did.

"They did it because Waihopai operates, in all but name, as an outpost of US intelligence on NZ soil..." he said.

He said the base should be closed immediately.

Murnane said outside the court, he believed the satellite aided crimes against humanity.

"I had to do this, it was necessary for me," he said.

"We wanted, in going into Waihopai, to challenge these warfaring behaviours and I think we have done this," he said.

"We have shown New Zealanders there is a US spy base in our midst."

Crown prosecutor Glen Marshall said the men deliberately and intentionally damaged the satellite cover hoping, rather than believing, their actions were lawful.

"It's not a belief, it's something less - a hope, an expectation, an opportunity,"