Constable Alexander James Cox, 30 was found not guilty of one count of recording intimate images without consent and one count of distributing intimate images without consent in Sutherland Local Court on Thursday.

Magistrate Holly Kemp said it was an accepted fact the officer showed pornographic images to colleagues, but on the available evidence it was not the constable and his former partner depicted in the video.

"The evidence is wholly indicative it was not (the complainant) on that video and could not have been her," she said.

The magistrate noted the video had never been produced to be viewed by the court or by the complainant for her to be identified.

The constable telling colleagues the woman in the video was his former partner was most likely a "throw-away joke" to bolster his image among other officers, Ms Kemp added.

"It is utterly in poor taste, grubby, juvenile and unacceptable," she said.

An additional charge of distributing intimate images without consent against Const Cox was dismissed on Wednesday after a key witness said an image allegedly shown to her did not in fact contain a sexual act.

The officer, the nephew of former NSW Police commissioner Mick Fuller, was accused of showing colleagues a video depicting "doggy style" sex with a woman wearing a collar and lead around her neck.

He told them the footage was of himself and his ex-partner, the court heard.

But neither of the men could remember seeing the woman's "distinctive tattoos", which Const Cox's lawyer Paul McGirr argued was firm evidence the video did not show the officer's former partner.

"People can't take tattoos on and off," Mr McGirr said.

One of those officers, Constable Zachary Barrett, acknowledged he only thought it was Const Cox's ex-partner in the video because of what his colleague had told him.

The magistrate accepted it was "utterly implausible" that Const Barrett would not have seen the woman's tattoos if they had been visible in the video.

Const Cox had been in a consensual sexual relationship with the woman, who cannot be legally identified, but she never gave him permission to film them having sex and did not recall him making any such recordings, the court heard.

They had sex on several occasions at his apartment at Engadine, in southern Sydney, during which a collar and lead that the woman owned were used at least once, she said.

Const Cox claimed the couple had never used the collar and lead during intercourse and that the woman might have mistaken them for a set of "silk ties" he bought, which were merchandise from the movie 50 Shades of Grey.

Ms Kemp accepted there were "gaping holes" within the police investigation, including failing to examine the complainant's phone or asking her to produce the collar and lead.

Mr McGirr told the court his client would be applying for costs, largely on the grounds police failed to properly investigate the matter.

A costs hearing has been set for September 16.

Australian Associated Press