An elderly woman was walking along canal path near to Victoria Park when a man came up to her before revealing his genitals.
Witness reports state the distressing incident took place at roughly 10.30am on 18 April.
Two concerned passersby informed Thames Valley Police of the incident.
They spoke with the victim who informed them of the shocking approach.
Since an investigation was launched into last month’s crime, one man, 50, of no fixed abode has been cuffed.
He has since been released on conditional bail while enquiries continue, Thames Valley Police state.
A Thames Valley Police spokesman said: “The victim in this case has not yet come forward, and so Thames Valley Police is urging her to do so.”
Investigating officer Detective Constable Annabel Wilmot of the Aylesbury Priority Crime Team, added: “We are continuing to investigate this third party report of an exposure incident on 18 April, but as yet, despite our best efforts, we have been unable to locate the victim.
“I am appealing for this person to please make contact with us as soon as possible.
“You can do so by calling 101 or making an initial report online, quoting reference number 43220166528.
“I would also appeal to anybody else who may have been in the area at around the time of the incident to please contact us if you believe you witnessed what happened.
“You can also call the independent charity Crimestoppers anonymously on 0800 555 111.”