Four animals rights activists face up to 14 years in jail after being found guilty of blackmailing companies who supplied Huntingdon Life Sciences.
Gerrah Selby, 20, Daniel Wadham, 21, Gavin Medd-Hall, 45, Heather Nicholson, 41, and Trevor Holmes, 51, were accused of orchestrating a campaign which ran between 2001 and 2007.
All five denied conspiracy to blackmail but Selby, Wadham, Medd-Hall and Nicholson were found guilty at Winchester Crown Court. Holmes was cleared of the charge.
One of the jurors refused to be seen in court while the verdict was announced after 33 hours and 48 minutes of deliberation.
Selby, Wadham and Medd-Hall were released on conditional bail, while Nicholson was remanded in custody until sentencing on January 19. The maximum sentence for the offence is 14 years imprisonment. Three other people - Gregg Avery, Natasha Avery and Daniel Amos - previously pleaded guilty to conspiracy to blackmail.
The hierarchy of the group, called Stop Huntingdon Animal Cruelty (Shac), used threats such as claiming that managers of the companies were paedophiles, hoax bombs parcels, criminal damage and threatening telephone calls to force them to cut links with the animal testing company.
The aim was to target suppliers or any company with a secondary link with Huntingdon Life Sciences (HLS), based in Cambridge.
One of the features of intimidation included sending used sanitary towels in the post, saying they were contaminated with the Aids virus, and personal campaigns against the management of companies including daubing roads outside their homes with words like "Puppy Killer".
Nicholson, from Eversley in Hampshire, was a founder member of Shac, who managed the "menacing" campaigns against the firms who were named on the group's website. The blackmail would only stop when they put out a "capitulation statement" to Shac saying they would not supply HLS, which conducts animal testing for the pharmaceutical industry.
Detective Chief Inspector Andy Robbins, senior investigating officer of Kent Police, paid tribute to the victims of the "systematic and relentless intimidation" which lasted for six years until arrests were made on May 1 2007.
