An animal rights activist has been convicted of sending a " shocking and offensive" package to Huntingdon Life Sciences which was emblazoned with a swastika.
A jury at Birmingham Crown Court found Andrew Kirk guilty of a single count of sending an obscene or indecent postal package.
Kirk, who was cleared of 17 other counts of the same offence, will be sentenced in December after being granted conditional bail.
His two-day trial was told that he sent a total of nine packages containing insults and graphic images of animals, including one delivered to the MP for Huntingdon, Jonathan Djanogly, and others to the Chief Crown Prosecutors in Durham, Humberside and Staffordshire.
He was also alleged to have sent a package to a parish councillor living near to a farm in Yoxall, Staffordshire, which breeds guinea pigs for medical research.
The jury accepted Kirk's argument that none of the letters was indecent or obscene, but decided that an envelope in which one of the letters was sent had been in breach of the law.
That package - mailed to HLS's site at Wooley Lane, Huntingdon - was addressed to the "sons and daughters of Josef Mengele" and branded the facility an "Auschwitz Laboratory".
Kirk had denied all 18 counts of sending obscene or indecent packages through the postal system.
The 46-year-old, formerly of Swanage Close, Middlesbrough, but now of no fixed abode, accepted that he had sent the items when he was interviewed by police.
Steven Bailey, opening the case for the prosecution, told the jury: "He thought that the 'extermination' of animals in the lab was akin to the Holocaust."