A man who stole a knife from a supermarket before fatally stabbing a man outside an Adelaide shopping centre will spend at least 20 years behind bars.

Key points: Shaun Falkiner stole the murder weapon from Woolworths minutes before the attack

Shaun Falkiner stole the murder weapon from Woolworths minutes before the attack Justice Trish Kelly accepted Falkiner did not intend to kill the victim

Justice Trish Kelly accepted Falkiner did not intend to kill the victim Victim's family says nothing will bring him back

Shaun Falkiner, 28, was sentenced to life in prison with a 20-year non-parole period for murdering Alexander Watts in the suburb of Elizabeth in city's north last year.

The Supreme Court previously heard Falkiner stabbed Mr Watts, 25, on a pedestrian crossing outside the shopping centre with a long-bladed kitchen knife he stole from Woolworths in the lead-up to the attack.

It heard that about 25 minutes before the fatal stabbing Falkiner had a confrontation with a woman he knew in the shopping centre.

The woman ran into a friend, Mr Watts, who was shopping in Big W with his partner.

The prosecution said Mr Watts then started to follow Falkiner through the shopping centre and yelled something like: "Why would you hit a woman?"

In the meantime, Falkiner had stolen a kitchen knife from Woolworths which had a 20-centimetre blade.

Alexander Watts died after he was stabbed in the chest at the Elizabeth shopping centre. ( Facebook )

Falkiner claimed he acted in self-defence because the victim had been following him.

Defence lawyer Bill Boucaut previously told the court Falkiner did not intend to kill Mr Watts and inflicted the stab wound as a "half-hearted warning shot".

During sentencing today, Justice Trish Kelly said she accepted Falkiner did not intend to kill Mr Watts.

"However the fact is you went into the Woolworths store shortly prior to confronting Mr Watts, you obtained a large kitchen knife, secreted it in your clothing and at the pedestrian crossing just outside the shopping centre you made a decision to return to that pedestrian crossing and stab Mr Watts," she said.

"The fact that you were prepared to forcefully thrust such a large knife into a vulnerable part of the body speaks an intention at the very least to cause grievous bodily harm," Justice Kelly said.

She said the Watts family had lost a much loved member.

"You must now pay for your decision to use that knife in those fatal few seconds as you crossed the pedestrian crossing that night.

"There is no excuse for ever introducing a violent weapon such as a large knife into any altercation."

Outside court Mr Watt's mother Belinda Bezzina said nothing would bring her son back.