The 17-year-old who cannot be named for legal reasons, stabbed Peter Duncan with a screwdriver he had earlier stolen.
The incident took place inside the doors of the shopping centre at Old Eldon Square on the evening of August 14.
Emergency services attended and the 52-year-old was taken to hospital where he sadly died from the single puncture wound.
Today (Monday), the teen appeared at Newcastle Crown Court where he pleaded guilty to murder.
Following the case, Detective Chief Inspector Jane Fairlamb, from Northumbria Police’s Homicide and Major Enquiry Team (HMET), said: “Our thoughts continue to be with Peter Duncan’s family and friends at what is an incredibly difficult time.
“This was a shocking incident, in which a much-loved family man was murdered in an unprovoked attack after a chance encounter.
“I want to make it crystal clear it can never be acceptable for anyone to carry a weapon on our streets – as this case highlights the consequences can be truly devastating.
“I would urge anyone who thinks otherwise to think again. Not only could you destroy someone else’s life and those of their loved ones – but also think of the impact on your life and that of your family and friends.
“I can assure you if you are caught with a weapon you will be dealt with robustly and put before the courts.”
Det Chief Insp Fairlamb added: “I would also like to take this opportunity to thank the public for their support at what has also been an upsetting time for the wider community.
“Incidents of this nature are not what we expect in our towns and cities – and nor should they ever be. I want to assure you we are committed to doing everything we can to ensure the streets where we all live and work remain among the safest in the country.”
The teenager, who cannot be named due to his age, also admitted theft and possessing an offensive weapon.
Sentencing will take place at Newcastle Crown Court on date to be confirmed.
The family of Peter Duncan have previously issued a statement in which they said: “Peter was a kind and caring man who was always first to help others.
"He was a devoted father, husband, son, brother, uncle and friend and loved by all who knew him. His death will leave such a huge hole in our lives and he’ll be deeply missed by us all.”
“Words can’t quite describe what life will be like without him. He had so much of his life left to live and he’ll be in our hearts and thoughts every day.”