Police have caught two teenagers accused of being involved in the Rolleston "drown him" assault case.

The assault took place on November 4 after a fireworks display.

The Star has learned that police have had a difficult job determining who was involved in the incident due to a lack of co-operation.

A 15-year-old says he was punched and kicked and then dragged to a water race, and had his head held under water while his attackers chanted "drown him".

Two youths, aged 15 and 16, have been referred to youth aid, a police spokeswoman said.

A youth aid officer will review the case, meet with the victim and alleged offenders and determine the best course of action, which could include charges.

Police are not seeking anyone else in relation to the assault which left the victim with a nasty gash on his face that required stitches and a night in hospital.

The Star has also learned a complaint about two officers involved in the case has been laid with the Independent Police Conduct Authority.

IPCA case resolution manager Monica Robbers said due to privacy issues it cannot confirm whether it received a complaint or give any other details about the officers involved.

Police have been tight-lipped over the investigation since the attack was revealed by the Star last month.

However, police confirmed a search warrant was executed at a Rolleston property. The Star has been told shoes and a cellphone were seized. But police would not discuss specifics about what was taken in the raid.

The teenager was assaulted when he allegedly refused to hand over his cap after he was confronted on Tennyson St at about 10.30pm.