A petrol bomb and death threats have been delivered to staff at a guinea pig farm and to the owners' family.
Several workers at Darley Oaks Farm at Newchurch, Staffordshire, which breeds animals for medical research, have also received threatening letters.
The remains of Gladys Hammond, 82, who was related to the farm's owners, were stolen from her grave in Yoxall last October and have not been recovered.
The incidents are believed to be the work of animals rights extremists.
Staffordshire Police say the latest attacks are being treated extremely seriously.
The daughter of one of the farm's owners had a petrol bomb left outside her home in Burton-on-Trent this week.
The petrol bomb and letters are being examined by scenes of crime officers.
Detectives investigating the grave desecration have arrested two men and one woman, who all remain on police bail.
Mrs Hammond was the mother-in-law of Christopher Hall, who part-owns Darley Oaks Farm.
The burial plot of Mrs Hammond, who was laid to rest more than seven years ago, was disturbed on 7 October 2004.