During an anti-vaccination protest on Wednesday (29/12) at a testing site in central Milton Keynes, an individual was seen to take equipment.
Officers believe the woman in this image has information about what happened.
An investigation is ongoing and no arrests have been made at this time.
Chief Inspector Graham Hadley, of Thames Valley Police, said: “We are carrying out a thorough investigation into the protest that happened yesterday.
“As part of our enquiries, we believe the woman pictured may have information that could help our investigation.
“If you recognise this woman, or if it is you, please get in touch with us by making a report online or calling 101, quoting reference 43210583457.
“Furthermore, we are also continuing to appeal for witnesses to this incident, anyone who has information or video footage, to please come forward and make a report to us if you haven’t already. You can do so by using the methods above.
“If anyone wishes to remain anonymous, you can contact the independent charity Crimestoppers by calling 0800 555 111 or via their website.”