The activists filmed several of their raids on firms
Four animal rights activists have been convicted of orchestrating a blackmail campaign against firms that supplied an animal testing research centre.
They used paedophile smears, criminal damage and bomb hoaxes to intimidate companies associated with Huntingdon Life Sciences (HLS) in Cambridgeshire.
The four, members of Stop Huntingdon Animal Cruelty (SHAC) from Hampshire and London, had denied the charges.
A fifth defendant was cleared by the Winchester Crown Court jury.
During a six-year campaign the group falsely claimed managers of the companies were paedophiles.
Clockwise from top left: Nicholson, Selby, Wadham and Medd-Hall
They also sent hoax bombs parcels and made threatening telephone calls to firms telling them to cut links with HLS.
One of the features of intimidation included sending used sanitary items in the post to the firms and daubing roads outside managers' homes with slogans such as "puppy killer".
Heather Nicholson, 41, of Eversley, Hampshire; Gerrah Selby, 20, of Chiswick, London; Daniel Wadham, 21, of Bromley, south London, and Gavin Medd-Hall, 45, of Croydon, south London, were found guilty of conspiracy to blackmail.
Another defendant, Trevor Holmes, 51, from Newcastle, was cleared.
Earlier, three other people, Gregg Avery and Natasha Avery, both of Hampshire, and Daniel Amos, of no fixed address, pleaded guilty to conspiracy to blackmail.
The court heard the defendants were part of SHAC, which was based near Hook, Hampshire, and targeted companies in the UK and Europe between 2001 and 2007.
It was told Nicholson, from Eversley in Hampshire, was a founder member of SHAC, who managed the "menacing" campaigns against the firms.
Selby, Wadham and Medd-Hall were released on conditional bail, while Nicholson was remanded in custody.
A man who worked for a company which transported animals for HLS said he still fears reprisals after being sent obscene packages.
"We received a lot of phone calls and letters [which] contained things like used condoms, used sanitary towels, razor blades and syringe needles claiming to be from people who are infected with AIDS," he added.
A spokesman for HLS said: "Freedom of expression and lawful protest are important rights in our democratic society but so too is the right to conduct vital biomedical research, or to support organisations that perform such research, without being harassed and threatened.
This conspiracy to blackmail involved the systematic and relentless intimidation of individuals
"The UK environment for such biomedical research has improved greatly in recent years; this is the direct result of positive action taken by law enforcement agencies to control animal rights extremism.
"As a consequence we have seen greater openness in the research community that must lead to improved dialogue and better understanding - animal research remains a small but essential part of such research."
The verdict on Tuesday came after seven days of deliberation.
One of the jurors refused to be seen in court while the verdict was announced.
Sentencing will take place on 19 January.
Det Ch Insp Andy Robbins, of Kent Police, told the BBC: "We are very satisfied with the outcome of this prosecution.
"This conspiracy to blackmail involved the systematic and relentless intimidation of individuals and their companies who the defendants suspected to be involved with HLS.
"There was a whole group of tactics used by SHAC and I would like to pay tribute to the many victims who have had to carry on their lawful business while living through this criminal campaign.
"The public should also be aware that money donated to SHAC in good faith was in fact being used to finance criminal conduct.
"SHAC and the ALF [Animal Liberation Front] are one of the same, there is no club, no rules of membership."
Dr Simon Festing, from the Research Defence Society, said: "One of the effects of animal rights extremism has been to scare scientists, to actually stifle any kind of debate and it's been very frustrating for us.
"We want to enter into a debate and a dialogue with the public about the ethics of this and we know it's a matter of concern.
"We want to be able to show people into research facilities especially where huge sums are being invested in making the welfare for the animals as good as possible."
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