The wife of a Perth man alleged to have been murdered during a confrontation over a stolen bike, has described seeing the blade of the knife a teenager used to fatally stab her husband.

Anna Levkovskaya was giving evidence at the Supreme Court trial of the teenager — who cannot be identified — on a charge of murdering 42-year-old Petr Levkovskiy on a Sunday morning in May last year in the southern suburb of Bull Creek.

The court has heard the couple, who had been married for 21 years, had decided to help a 10-year-old boy look for his stolen bike after hearing him cry out outside their home.

They both got in their car, and after a few minutes found the teenager on nearby a corner with the bike.

‘He held him gentle, not tight’

Ms Levkovskaya said her husband got out of the car and she heard him say “let’s talk” to the teenager in what she described as a “not aggressive” and “calm manner”.

She told the court she remained in the car driving it slowly around a corner but saw her husband with his arms around the teenager.

“He held him gentle, not tight,” she testified.

Ms Levkovskaya said she then parked her car, so it did not block traffic, before getting out and seeing the teenager.

“I saw his eyes … there was eye contact,” she said.

“I saw a piece of blade. He put a blade into a holder case. I saw the action.”

Ms Levkovskaya said everything happened “in a just a few seconds”.

“For me it’s like slow motion … it’s very very hard.”

The teenager has admitted he stabbed Mr Levkovskiy in the abdomen, but denies he intended to kill him, instead claiming he meant only to stab him in the leg.

The court has heard the weapon he used was a filleting knife with an 18-centimetre blade, that was held in a sheath.

Prosecutors said the teenager had come into possession of the knife months earlier, and he had been photographed two days earlier wearing the same type of knife, in its sheath, attached to his belt buckle.

Ms Levkovskaya will continue her evidence when the trial resumes on Monday.