Dylan Voller joined a small crowd protesting against the conditions in NT detention centres as the Royal Commission into Juvenile Justice resumed hearings in Alice Springs on March 13.
Footage broadcast on the ABC showing Voller being tear-gassed, spit-hooded and shackled to a restraint chair prompted Prime Minister Malcolm Turnbull to call the inquiry.
Speaking outside the commission, Voller said he wanted to support the other young people giving evidence.