Chilling police interview footage has showed the moment a man accused of a deadly knife attack in an Adelaide real estate office told detectives he “wanted to kill someone” that day.

In the disturbing video obtained by 7NEWS, 32-year-old Shaun Michaels Dunk can be heard making an admission just hours after he allegedly murdered Julie Seed and attempted to kill her workmate, Susan Scardigno, at their Plympton real estate office.

“I went out with the intention to kill someone today. It’s just been something that I wanted to do for a long time, I guess,” Dunk told detectives in a four-hour long police interview released by the Supreme Court of South Australia.

Appearing calm and composed during the interview, Dunk described scoping out his alleged target, preferring a small business with few employees.

He found the two women working alone in the Plympton real estate office.

“It’s an easy target, I guess. I thought it would just be, like, easy people to attack working there. I just thought that was something that I wanted to do, so I don’t know,” he said.

When asked by police whether his intention was to continue stabbing, Dunk replied, “I don’t know, just until I felt satisfied.”

You’re stabbing someone, you know what I mean? It’s just pretty, like… it’s a commitment,” he said.

The accused was armed with a knife and meat tenderiser which he used to subdue Seed before stabbing her.

Dunk also admitted he was almost caught with the weapons the day before the attack.

Seed died at the scene while Scardigno survived with five knife wounds to the chest.

Dunk is standing trial to determine whether he was mentally competent at the time of the crime.