A letter bomb which injured a woman at a DNA testing company may have been sent by animal rights extremists.
The area was declared safe by bomb disposal experts
The worker at Cellmark in Blacklands Way, Abingdon, Oxfordshire, suffered a minor injury to her hand.
Police said the name Barry Horne - an animal rights campaigner and convicted fire-bomber who died in 2001 - was written on the envelope.
Another package was sent to a firm in Culham but failed to explode. Police believe the incidents are linked.
A police spokesman said: "The device has been sent for forensic examination but a reference to a well-known animal rights extremist, Barry Horne, on the back of the envelope, leads officers to make this a priority line of enquiry.
"It also emerged this afternoon that a second company, in Culham, had contacted Thames Valley Police after they too received a suspect package in the mail.
"In this instance the device was not activated and no one was hurt. The two incidents are being linked."
Police are now warning companies and individuals to be vigilant when dealing with incoming mail.
On its website, Cellmark describes itself as a leader in DNA testing.