A Canberra man accused of plotting to rob a southside supermarket admitted planning a "smash and grab", but said he decided not to use weapons.

The 34-year-old man told police he "knew the law" about robberies and thefts, and planned the job so as to make it a lesser charge if caught.

But the accused is on trial in the ACT Supreme Court charged with conspiring with another man to commit aggravated robbery on the Woolworths at Kambah Village in January last year.

Neither the accused or his co-offender can be named for legal reasons, and The Canberra Times will call them Persons A and B respectively for the sake of clarity.

Person B pleaded guilty to his role in the plan, and received a discounted sentence for agreeing to give evidence against Person A.

The Crown alleges the pair planned to rob the supermarket with a knife and a pinch bar at closing time, stealing the day's takings and fleeing the area on push-bikes.

But the defence says the accused never intended to use violence or threats.

The two men never got as far as the front door, with police "jumping out of some bushes" and arresting them.

Person A agreed to an interview with police a short time later.

"I had no intention of doing this armed," he said.

"My intention was, I will be straight honest, my intention was I was going to wait until the shop closed, 10 o'clock, I was going to smash through the window of the shop ... a smash and grab, you might say.

"At no time, I think it entered my mind a couple of times to do it armed, but I thought I don't need to do it armed."

The accused man said he was in the store a week earlier buying bread and milk when he saw the cash bags and began formulating a plan. Person A told investigaters he "knew the law" in relation to robberies and thefts, and thought his plan fell into the latter category.

"I thought it was demand by menace, if that is even a charge," he said.

When told the other man was arrested in possession of a knife, Person A denied any knowledge of the weapon and said he was "a bit shattered".

Person A said they met three years ago and bonded playing chess, but he didn't "know him, know him".

"Could have been a f**king serial killer for all I knew," he said.

The trial before Justice John Burns continues.