A police officer who conducted 19 strip searches at a 2018 music festival has admitted to an inquiry that all of them may have been illegal.

The senior constable made the admission under questioning at the Law Enforcement Conduct Commission’s investigation into the use of strip-search powers by the New South Wales police on Tuesday.

The commission heard only one of the searches conducted by the officer found any drugs: a single diazepam tablet, a drug used to treat anxiety and depression, prompting the commissioner, Michael Adams QC, to ask whether police were “just taking a punt” on who they subject to a strip search.

The officer – whose name is subject to a non-publication order – worked at the 2018 Splendour in the Grass festival near Byron Bay. The police watchdog is investigating whether police at that festival conducted an illegal strip search on a minor by failing to have a parent or guardian present.

In NSW, police are required to meet a threshold for urgency and seriousness when conducting a strip search in the field. Under questioning by the commissioner on Tuesday, the officer admitted none of the 19 strip searches he conducted at the festival could have been justified because they did not meet that threshold.

Adams asked the officer under what circumstances – apart from a suspicion someone was hiding drugs in a body cavity, which police are not allowed to search – it would be urgent for an officer to conduct a strip search at a music festival.

“I can’t think of any, actually,” the officer replied.

“There was no urgency at all in any of these searches, was there, now you’re looking back?” Adams asked. “For you to do a search in the field you have to have [met] both seriousness and urgency [and] there were no urgency was there?”

“No,” the officer replied.

“From which it follows there were no circumstances in which [the search] was lawful?” Adams said.

The senior constable agreed, saying it had been “a massive learning experience”.

Adams questioned how police defined that threshold, and suggested there was insufficient training given to officers conducting searches in the field.

“You’re told of the LEPRA rules, you’re told of the sections [but] not actually given the contents of what might be urgency or what might be seriousness, you’re just told of the section, that’s the training [and] you’ve got to work it out for yourself,” Adams said.

Saying he did not want to put a senior constable’s “head on a stake”, Adams questioned why the NSW police did not have a “corporate position” on what constitutes seriousness or urgency.

“Am I right in saying, again, in your training [that] there is not real attention given to what might constitute seriousness?” Adams asked.

“Yes I agree,” the officer said.

The officer was giving evidence on the second of a four-day inquiry into the exercise of strip search powers by police in NSW. The inquiry previously heard evidence that drugs were found in less than 10% of the 143 strip searches carried out at the festival, and on Tuesday Adams questioned how police were making determinations about who to search, asking whether they were “taking a punt”.

The officer agreed that it was “not a good success rate” but said it was “more than a punt”, saying police considered things like body language, whether a person was “fidgeting” and whether a person made a “U-turn” when they saw a drug dog.

On Monday the inquiry heard that a 16-year-old girl was left fearful and in tears after she was forced to strip naked in front of police at the 2018 Splendour in the Grass festival. In the case of strip searches on a minor, a parent or guardian must be present unless an immediate search is deemed necessary to protect the person or prevent evidence being destroyed.

The senior constable – who did not conduct the search of the 16-year-old but conducted other searches on minors – admitted on Tuesday that he had not been aware of the requirement while working at the festival and that police working at the event had not given prior thought to what they would do if a parent or guardian was not available.

The inquiry also heard the officer had given what Adams described as “seriously careless” information to the commission before giving evidence. In a document supplied to the commission, the officer had said the 16-year-old girl had admitted to smoking cannabis before the search. However this information was not recorded at the time of the search and the officer confirmed he had no memory of that occurring.

“It was an error,” the officer said.

Adams said the error was “capable of being very misleading” and questioned whether it was a “construction”.