Benjamin Ladd, previously reported to have lived in Frenchs Forest in NSW, fronted an ACT Magistrates Court hearing on Monday to face one charge, to which he pleaded not guilty.

The prosecution alleged that in May 2020, while putting a patient to bed at a Weston facility, Mr Ladd lifted the patient's top to expose her right breast before sucking her nipple.

At the time, a fellow carer who worked with Mr Ladd, 43, left the room for a few seconds as she took a mechanical lifter, which helps put patients into bed, out into the corridor.

She then re-entered the room and saw the patient's breast exposed and the defendant's face moving away from the patient's chest.

Prosecutor Sam Bargwanna accepted it was a circumstantial case, and there was "no direct evidence of the Crown allegation".

Defence lawyer AJ Karim said the alleged offending "simply didn't occur".

Mr Karim said it was conceded that the patient's breast was exposed, but it was in the context of "Mr Ladd performing his lawful duties of attending [the patient]".

"When your honour accepts the totality of the evidence, the Crown case must fail," he said.

Mr Karim said the witness account was speculative and had "very little probity value" because the alleged offending could not have happened in the time she claimed.

"She doesn't see touching of the breast, she doesn't see kissing of the nipple, she doesn't see licking of the nipple," he said.

"By seeing the erect nipple, she has come to the conclusion that the defendant must've kissed it. Speculative reason, she simply didn't know."

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In her recorded evidence in chief played to the court, the complainant, a high-care patient with mobility issues and dementia, was asked a number of times about whether Mr Ladd had touched her in the chest area.

"Nothing happened ... he managed to pinch me on the back," she said.

She added that there was "nothing to talk about".

Jennifer Stone, a forensic biologist at the Australian Federal Police who conducted examinations in the case, told the court that her DNA analysis result from crime scene samples "strongly supports that Mr Ladd is the source of the DNA profile obtained".

Ms Stone also said saliva tests in relation to two of the three areas swabbed gave strong positive results that it was only one person, being Mr Ladd.

However, during cross-examination she conceded it was possible that the saliva tests could have been false positives, and that the RSID test method used was not conclusive as it did not target saliva but only the alpha-amylase enzyme in saliva.

Ms Jones also said such deposits of DNA and saliva could occur while talking over the body of someone or via secondary means without touching anyone.

The court also heard that the complainant was on medication at the time that led to excretions from her breast that also contained the enzyme.

The defence called on molecular geneticist Dr Brian McDonald, who spoke about the probability of secondary DNA transfer between Mr Ladd and the complainant during care.

He also testified the saliva test was presumptive only, rather than definitive.

Magistrate Glenn Theakston found Mr Ladd not guilty, saying the witness account was "bordering on implausible".

Mr Theakston said while he did not understand what Mr Ladd was trying to do - Mr Ladd had told police he was trying to make the patient more comfortable - there was enough doubt that he would not hand down a guilty verdict.

"That is, the events observed [by the fellow carer] were events she did not fully understand," he said.

"In the process of caring for the complainant, the defendant did briefly expose her breast, but there was nothing untoward about that.

"His DNA located on her breast could have been placed there simply by his proximity."

Mr Ladd, who the court heard had no criminal history and had worked at the Weston facility without incident, was supported by his father in court.

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