As former Northern Territory Police constable Zachary Rolfe defends his use of force at an inquest into the death of an Indigenous teenager, his claims of racism in the ranks has prompted a probe of police culture.

Rolfe shot Kumanjayi Walker, 19, three times while on duty in the remote community of Yuendumu in November 2019 and was acquitted of murder in a five-week trial.

Giving evidence at an inquest into Walker’s death, the ex-officer accuses NT Police of having an ingrained racist culture.

Rolfe said racism was unacceptable but it was normalised and exhibited almost daily within the force.

He said the NT Police Territory Response Group issued an annual award to its officers, using a derogatory name for Indigenous people.

Reflecting on racist text messages he sent, shown at the inquest in 2022, Rolfe said language he used to describe Indigenous people would have caused hurt to some.

“That killed me. I’m sorry for that,” he said.

NT Police Commissioner Michael Murphy said on Tuesday the force would investigate Rolfe’s claims of racism but it was “too early to say” what form the inquiries would take, as police had to respect the ongoing inquest.

“There will need to be an inquiry undertaken and a search for the truth to find out exactly what basis, if any, of the assertions made … in the court are true or not,” Murphy told reporters.

While conceding Rolfe’s evidence would hurt the Aboriginal community, he rejected calls for the Territory Response Group to be disbanded, arguing racism was not widespread in NT Police.

“When I go to Alice Springs and the other stations around the Territory, I do not see those behaviours, I don’t hear those comments,” he said.

“Sometimes we don’t always get it right and there are pockets of people who make mistakes.

‘It’s about learning from that, not just as individuals, but as an agency.”

Rolfe took the stand again on Tuesday and faced questioning about his text-message history and use of force as a police officer.

Rolfe’s legal team has argued questions regarding eight use-of-force incidents, his police force application and some of the racist texts should not be admissible.

Coroner Elisabeth Armitage has compelled Rolfe to answer questions about his history.

The inquest was shown footage from an arrest in 2019 in which Rolfe and another officer crashed into a suspect, causing him to ricochet into a wall, resulting in a head injury.

Rolfe said he was acting in response to seeing the man headbutt and punch a woman and conceded his actions during the incident were affected by anger as a result of witnessing a suspected domestic violence incident.

Later, Rolfe messaged a paramedic he was close with about the incident, boasting he “mashed some dude’s face up against a wall”.

Rolfe denied he was using violence as a way of coping with the pressures of the job after a question from counsel assisting the coroner Peggy Dwyer, instead claiming it was a way of “venting frustrations”.

“Obviously, that job is one of those jobs that I was talking about before that does create anger seeing a woman get assaulted by the main person in her life who should be protecting her,” he said.

The inquest was told Rolfe was suffering from insomnia while working in Alice Springs and on occasion would self-medicate with cannabis edibles.

Rolfe said it was common for officers to deal with mental health issues on their own while some would use stress leave to “fudge the system”.

“I believe someone’s been off for five years and got a degree in that time,” he said.

Dwyer said the abuse of the system had to stop “because it makes it so much more stressful for other officers on the ground”.

Rolfe is due to continue giving evidence on Wednesday.

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-AAP