Officers want to speak to the man pictured, with the force saying they “firmly believe” he has information that could be useful to the probe.
He is understood to have been in the Aylesham area on 28 April – the day after Ms James as murdered.
The popular community support officer was found dead in Akholt Wood near her home in Snowdown, a hamlet in Kent, last month.
A post-mortem has found the 53-year-old died from “significant head injuries”, according to Kent Police.
The force released the image of the man they would like to speak to for the murder probe late Friday morning.
“We firmly believe he has information that could help this investigation and we urge him to come forward,” Assistant Chief Constable Tom Richards said.
“We are also appealing to the public or anyone who knows this individual to please come forward with his details. Perhaps he lives near you, perhaps you work with him or perhaps he visits your local shop to buy food.”
He urged members of the public to get in touch with police to help officers “find the answers Julia’s family deserve”.
Later in the day, ACC Richards told a press conference:“I’m not saying here and now that he is a suspect, but he is of crucial importance to the investigation.”
He told reporters in Folkestone: “Somebody knows who that man is. We desperately need you to make contact with us and help us identify who that person is.”
He added: “If that person is watching, please make contact with us. We believe that you have crucial information.”
ACC Richards said at the conference on Friday afternoon the local population had been “absolutely superb” in supporting the probe into Ms James’ death, with more than 1,000 pieces of information provided by the public – which he called “absolutely incredible”.
“But I need someone to do the right thing, and give us the information that we need so that we can help bring justice to Julia for her family and for Julia herself.
Speaking to local radio early on Friday before the photo was released, Kent Police’s chief constable said the force was not clear on a motive, but was looking into this with an “incredibly broad focus”.
CC Alan Pughsley also said police were “not 100 per cent sure” what weapon was used to murder serving PCSO James.
He told Breakfast on BBC Radio Kent: “It was a severe traumatic injury to Julia, but it’d be wrong to talk about what style of weapon was use until we, one, have the suspect, and two, have some more detail around the weapon we believe that was used.”
When asked whether the killer may have struck before, CC Pughsley said early on Friday morning: “I don’t know, because we don’t know yet who the killer is. I hope not.”
Crimestoppers are offering a reward of up to £10,000 for anonymous information that leads to her killer being convicted.
Mick Duthie from the charity said: “Crimestoppers is here to help people who – for whatever reason – won’t or can’t speak directly to the police, but want to do the right thing.”
ACC Richards from Kent Police said: “We’re still waiting for that critical phone call or piece of information to help solve this investigation.”
He added: “We have a large team of specialist detectives working on this case but there is someone somewhere who knows this man in the picture, or who knows something about the day Julia died.”
Anyone who recognises the man is urged to contact Kent Police on 0800 0514 526. Witnesses and anyone with any other information, CCTV or dashcam footage have been asked to submit details online.
Additional reporting by Press Association