Arnopp took the stand yesterday on the fourth day of Gilling's retrial for Mr Waipouri's murder, which Gilling has denied.
He told the court how the two had punched and kicked the 39-year-old in an alcohol, cannabis and party pill-fuelled rage on the night of December 22, 2006.
He is serving a jail sentence for his part in the murder - but Gilling, 18, never had any intention of owning up, he said.
"In a conversation I had with Andre Gilling during the trial he said a few things that were just like he didn't give a f*** eh."
But both carried out the murder at Mr Waipouri's Rangitikei Street flat that night - Gilling was even the instigator, he said.
"Andre said f*** it let's kill the c***.
"I'm not sure what Andre's buzz was, he knew what he was up to though . . . we killed him, both of us did it. His actions and his laughter and joking about it (afterwards) suggested that he was proud about it, which he is."
Arnopp told the court how he earlier protected and covered up for Gilling after he freaked out in the police cells - but he would not call them friends.
He was just doing what was right in giving evidence now, he said.
He always intended doing it, despite being convinced by a fellow inmate to ask for money in return for giving evidence, he said.
"It's you fellas' job to lock him up, if he gets out and does it again, it's you fellas' fault.
"Because that's what he's going to do anyway."
In cross-examination by defence lawyer Mike Antunovic, Arnopp said he felt like the one on trial.
"You already know what I've done, I already told you. . .I'm just saying that it wasn't just me.
"You're calling me a liar and Andre's got just as much blood on his clothes as me.
"You're defending the liar so are you the liar?"
The court heard how Arnopp had known Mr Waipouri for about three years but Gilling had only met him for the first time that night.
Arnopp said Mr Waipouri would still be alive if the two men had not been there together that night.
And the accused was not asleep at the kitchen table while he carried out the attack on Mr Waipouri, he said of Gilling's claim.
"We both took part in the murder of Stan, he [Gilling] wasn't asleep . . . he was right there from the start, right from word go.
"There was blood everywhere, um, over both of us . . . I think from the first attack he was pretty defenceless."
The trial continues today.