A boy who was with two teens before they allegedly killed a West Auckland dairy owner has described seeing one of the alleged weapons stuck to a household fridge.

The 14-year-old witness was interviewed by police the day after the incident, which left Arun Kumar bleeding to death from a neck wound on the floor of the Railside Dairy.

The recording of that interview has been played for the jury in the High Court at Auckland today.

A 14-year-old boy is on trial charged with murdering Arun Kumar, while his 13-year-old co-accused faces a charge of manslaughter after the June 10 incident at the Henderson dairy almost a year ago.

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The pair, who have name suppression, also face counts of assault with intent to rob.

In a recording from the interview, the witness described seeing a camouflage switch blade allegedly used in the attempted robbery magnetised to one of the defendant's fridge.

"I saw it a couple of times before the stabbing happened.

"It had this magnetised bit on it so you can stick it to the fridge...that's where I saw it.

"It was pretty sharp."

He also described a pole with two spikes.

The witness was also asked to identify his friends in stills from a CCTV camera recorded on the morning of Mr Kumar's death.

He said he was "100 per cent" sure it was his friends in the images.

One of the images showed his friend carrying the pole, he said.

The witness was unable to describe a third person pictured in the images, but said that person's hat and shoes were similar to his own.

Earlier today, another interview with the witness was played for the jury in which the teen spoke of how a trail of blood led police to his friend's door.

Their friend, whose name is also suppressed, initially told police he was not there and saw the aftermath because he was going to the murder-accused's house that morning to pick up his school uniform.

But he admitted this morning that was a "big lie".

The Crown said he followed the pair to the dairy on the morning of the incident, which he disclosed in a later interview.

"As soon as I got to his house he told me everything.

He just left trails of blood everywhere and the cops knew straight away it was him," the boy said.

"He told me he stabbed him ... he was just panicking. He was just so freaked out he couldn't even talk."

The witness said the 14-year-old defendant's upper body was covered in blood, as was a bag he was carrying.

"Just before he had that shower his mum walked in. That's when everything started to get a little bit nasty," he said.

The older defendant explained to him what had happened.

"The friend he was with actually forced him to go with him.

"He was the one that was forcing [him] to do it," the witness told police.

"[He] had nothing to do but self-defence, because the man grabbed him I think he just got scared and swung a bit too early."

The trial before Justice Graham Lang and a jury of six women and six men is scheduled to last about a month.