Western Australia's Corruption and Crime Commission is holding a public hearing into alleged police brutality at the Broome lockup.
The inquiry is examining two instances of alleged misconduct by the same officer in March and April this year.
CCTV vision of the first incident shows the constable, whose name has been suppressed, taking an 18-year-old man into custody using a neck lock which is against police protocol.
In the second incident, a 30-year-old Aboriginal man taken into custody throws a surprise punch at the officer.
The 31-year-old constable reacted by throwing several punches of his own and dropping his knee twice into the man as he lay on the ground.
The man's body appears to go limp and he is dragged into the station.
It is alleged the police officer told the man he "punched like a faggot."
The shift sergeant later ordered officers to take the man to hospital but that never happened.
He was later treated for a broken finger and swelling.
The inquiry has heard the constable could face criminal charges as a result.
It is alleged a number of police, including senior officers, witnessed the use of force on both occasions and did not intervene.
The counsel assisting Gail Archer said the inquiry would investigate the use of excessive force but its main focus was on the actions of supervising officers, and why those on duty did not intervene.
At the opening of the inquiry, the CCC's Roger Macknay says it was important police uphold certain standards.
"Each of us owe a debt of gratitude to [the police] however they are a disciplined force and its essential for the upholding of the rule of law that discipline is maintained, even in trying circumstances," he said.
After viewing the CCTV footage, the Police Commissioner Karl O'Callaghan demanded the constable show cause why he should not be fired.
He was served with a notice of intention to remove but has since resigned from WA police.
The Commissioner also stood down two other officers but one has since been re-instated.
The CCC has summonsed 13 police officers from Broome to give evidence.