Manslaughter accused Sonny Avon Rehu was described as "carefree, happy, and caring" by a witness, the defence reminded a High Court jury today at his trial in Christchurch.

Defence counsel Mark Callaghan also told the jury there were other incidents that could have caused a mild brain injury suffered by Shaun Finnerty-Gallagher, found dead in a Riccarton park in February last year.

Rehu and co-accused Thomas Tihema Christie faces charges of the manslaughter and indecent assault of the 16-year-old after murder charges against the pair were withdrawn.

In his closing address, Mr Callaghan said Rehu told police that Mr Finnerty-Gallagher had run into or collided with a tree.

He had also been tackled outside a liquor store when a shoplifting raid failed.

But he said Rehu had been protective of Mr Finnerty-Gallagher throughout the day before the death occurred.

He said Rehu had not done any act that caused Mr Finnerty-Gallagher's death, or helped Christie carry out the assault "to such an extent that the injury was a causative factor in his death".

"Mere presence at the park is not enough. The crown has to prove that he did something actively. And they can't."

Rehu's saliva had been found on Mr Finnerty-Gallagher's body, but the Crown could not discount the possibility of innocent transfer, Mr Callaghan said.

In a recorded conversation, Rehu said he did not know how it got there, and added: "I know I am not like that."

Rehu and Christie deny charges of manslaughter and indecent assault.

Other defence closing addresses will be held tomorrow.