The second assault, on Dylan Voller, the detainee who appeared in the notorious Four Corners footage in a spit hood and manacled to a chair, was considered serious enough by authorities that police were called to investigate.

The former acting general manager of Don Dale Youth Detention Centre, John Fattore, said the two attacks took place several months apart.

However, he absolved himself of blame for the re-employment of the guard, saying he trusted senior staff with their assessment of the officer.

Counsel for Voller, Peter O'Brien, attacked Mr Fattore for not personally interviewing Voller even after he had seen video of footage of him being assaulted by the guard.

Mr O'Brien accused Mr Fattore of "fundamental failure" in his role as the senior officer in not acting quickly to protect detainees.

The commission also heard allegations that another jail worker at the Territory's other youth jail, the Alice Springs Youth Detention Centre, had been the subject of claims he was "flirtatious" with detainees and made numerous remarks of a sexual nature to male and female detainees.

Among the comments contained in an email chain referred to commissioners, the staff member was alleged to have told detainees, "you just want to touch my dick, your gay" and when cautioned, he told supervisors "I am not the only (guard) talking like this to detainees".

But the Professional Standards Unit (PSU) only became involved in addressing his behaviour after he was alleged to have sexually harassed a female member of staff.

"There was all of this information that was circulating, but the incident that actually sparked your investigation concerned the sexual harassment of this man of another staff member, is that correct?" counsel assisting the commission Peter Callaghan asked.

"That is correct," Mr Fattore said.

Earlier, Trevor Hansen, a former shift supervisor at Don Dale, told the commission that detainees routinely threatened they would attack his children.

"A lot of the time we got spat at. We got things thrown at us," Mr Hansen said.

"A lot of the times they would want to punch you. That was basically daily life.

"A lot of the times the detainees would say I am going to blah blah your daughters and all this sort of stuff, and you had it thrown at you just about every day."

Derek Tasker, a former officer in charge at the Territory's second youth jail, the Alice Springs Youth Detention Centre, said there had been about 20 escapes.

Late on Tuesday, Commissioner Margaret White issued a warning concerning reports that young people, both in jail and out, were being intimated not to give evidence to the royal commission.

She said if true, such actions were against the law.