An apparent confession of a man who had moments before being arrested and charged with murder have been played to a High Court jury.

Adrian Reginald George Phillips, 24, is standing trial in Hamilton. He is facing one charge of murder in relation to the death of Bayden Williams, 20, who was found dead on the Kopu-Hikuai Rd on the evening of Wednesday, August 5, 2020.

It is alleged Phillips rammed Williams' vehicle off a twisting stretch of road. When Williams climbed up a bank back to the roadside, about 7pm that night, Phillips fatally injured him by shooting him three times in the shoulder, thigh and head with a shotgun.

The Crown contends Phillips was in a murderous rage when he fired the shots. His defence counsel says Phillips fired the shots in self-defence, because he believed Williams was coming at him with a knife.

On Tuesday afternoon, the jury heard evidence from Detective George Sanson who was part of the Armed Offenders Squad unit dispatched to Ngatea to arrest Phillips, not long after his then-girlfriend Macy Randall called the police to tell them he had shot someone.

Sanson had been nominated 'OC Suspect ... I was the one to arrest the suspect if the opportunity arose”.

Soon after their arrival at 9.20pm that night, Phillips was arrested without incident. Sanson read him his bill of rights and, because he had to keep his hands on his gun at all times, used his mobile phone to record their ensuing conversation.

'I f...ed up big time. I shot someone,” Phillips is heard saying at the start of the recording.

'Who?” asks Sanson.

'Bayden.”

'Who is this Bayden to you? Is he a buddy?”

'No,” Phillips replies.

A short time later Phillips tells the detective he had thrown his 12-gauge shotgun into the Piako River.

Why did he shoot someone, the detective asked.

'I don't know why,” Phillips replied. 'I wish I could take it all back. I'm so sorry.”

One of Phillips' possessions at that moment was a small bag containing some 'medical marijuana”.

'It's to help me stay calm. I have been trying not to depend on it lately,” he said.

He added he had been 'struggling with my mental health” and was attending fortnightly appointments with a psychologist.

Was the shooting something he had planned, the detective asked.

'No ... I did not even feel real. I'm extremely mentally unwell. This all feels like a big dream.

'Is it the first time you have felt like this?” asked Sanson.

'This is the worst time I have felt like this. It's not the first time,” Phillips replied.

A short time later Phillips revealed he had recently taken a shower and had left the clothing he was wearing at the time – shorts and a red, white and blue shirt with the word 'Reckless” printed on the front – on the bathroom floor.

'I did not know what to do. I felt gross.”

And later still:

'Obviously I lost my temper, and had the gun in the back [of my ute].”

'What did you get angry for?” asked the detective.

'I just can't tolerate all the wrong in the world,” Phillips replied. 'Sometimes I just can't manage my temper, and I don't know why.”

Both he and Williams had both been doing 'a bit of silly driving” that night, he said.

'I just wish I didn't run into him anymore ... Then he goes to pull a f...ing knife on me.”

Then Phillips is heard to whisper: 'I got the gun and I shot him.”

The detective asks him to repeat himself. 'I got the gun and I shot him,” Phillips says more loudly.

'I'm so sorry. I don't know if he's gone or not. I don't know what to do. It's all a big f...ing balls-up.”

Just before the recording ends Phillips is heard to ask: 'Am I going to end up in Henry Bennett?”

The Henry Rongomau Bennett Centre is the secure mental health facility at Waikato Hospital.

The trial continues.

-Stuff/Mike Mather.