Police investigating the murder of community support officer Julia James say a man they wish to speak to was seen in a “very relevant location”.
It came after detectives released an image of the person they believe is of “crucial importance” to the inquiry.
The PCSO was found dead in Akholt Wood near her home in Snowdown, Kent, on 27 April.
The 53-year-old died from serious head injuries while out walking her dog Toby, who was found unharmed by her side.
Assistant chief constable Tom Richards from Kent Police said he thought the man in the photograph, taken the day after her killing, was “key to unlocking” to what happened.
He said: “This man was in a very relevant location… and I have reason to believe that he will have evidence or information of crucial importance.”
Mr Richards added: “I’m not saying here and now that he is a suspect, but he is of crucial importance to the investigation.
“Somebody knows who that man is. We desperately need you to make contact with us and identify who that person is.
“If that person is watching, please contact us, we believe that you have crucial information.
“We need someone to do the right thing and help us.
He went on: “We are, of course, interested in many individuals but this individual is a big frustration to the investigation because we don’t know who they are and we desperately need a name so that we can identify them.”
Asked if the man should be approached, he said: “I’m not asking members of the public to approach this individual, I’m encouraging you to provide information to Kent Police so we can progress it.”