Sydney underworld figure Abuzar Sultani said he believed it was "me or him" when he shot fellow Rebels gang member Mark Easter during a meeting gone wrong.
Easter had requested Sultani buy a large amount of the drug precursor pseudoephedrine, which he did not want to do, prompting a tense interaction between the men in June 2015.
During the meeting, Easter was acting erratically and looking at him with "crazy eyes", Sultani told a Supreme Court sentence submissions hearing on Wednesday.
"I was thinking, 'It's me or him'," Sultani said.
"He had the firearm and I felt like an idiot that I'd left myself exposed.
"I leaned forward, I grabbed the firearm."
Sultani said he shot Easter, causing him to slump over a chair, after which he shot him several more times to ensure he was dead.
Mr Easter's body was found dumped on a fire trail with a bag tied around his head, having been left in a bathtub with ice for several days before being moved.
Sultani has also admitted to being involved in the murders of Penrith Rebels enforcer Michael Davey, drug dealer Mehmet Yilmaz and mafioso Pasquale Barbaro.
Barbaro was shot to death by Sultani and another associate, whom he refused to name when questioned by the prosecutor.
"I've got to worry about myself ... I can't answer that ... I'm in jail," Sultani said.
"I'd rather get a contempt than answer that."
The associate first shot Barbaro four times in the forearm, chest, armpit and back before he exited his vehicle and attempted to flee, the court heard.
Sultani pursued him and shot him several times in the back of the head, however Sultani claimed by that time Barbaro had already collapsed and was "lifeless".
He said adrenaline and "personal hatred" motivated him to shoot Barbaro, despite him most likely already being dead.
Sultani and a group of men had earlier assaulted Barbaro, prompting death threats in retaliation.
In 2016 when the murder occurred, Sultani was running an organised crime operation centred around the drug trade.
Sultani said the group saw themselves as "bad blokes, but the better of the bad blokes".
"I was dealing drugs at that time. And I was making good relationships with people," he told the court.
"We used to get harassed by the police a lot."
Sultani said he would frequently be stopped and searched by the NSW Police organised crime task force, Raptor Squad, and that him and others couldn't even go to the beach without drawing attention from police.
In one text message, Sultani wrote to associates: "let's survive this taskforce so we can tell our grandkids ... we shook Sydney bro".
