The 18-year-old has been arrested after the death of a 71-year-old store owner, identified as Linford Feick, in Darwin.
The local community is reeling after Mr Feick allegedly confronted a thief and was stabbed at the Nightcliff Friendly Grocer about 5.15pm on Wednesday.
The teenager - who turned 18 days ago - was taken into custody after handing himself in shortly after midnight, but has not yet been charged.
Police confirmed he was on bail for "serious matters" with conditions to remain in a remote Northern Territory community.
The tragedy comes about two years after a Darwin bottle shop worker was killed by a man out on bail, prompting a tightening of NT laws.
Police allege the suspect fled on a bicycle after the stabbing, which occurred when Mr Feick told him to return items taken from the store.
Shoppers provided first aid before emergency services arrived, but he died at the scene.
"When this incident occurred and the male offender had left the location, the Northern Territory police surged with all available resources ... into the Darwin community," Assistant Commissioner Travis Wurst told reporters on Thursday.
"The family of the person was located, and through that ongoing engagement ... that person handed himself into police, which is a good outcome for the community."
Police said the 18-year-old had been granted bail in April, but did not disclose the charges.
"The matters are serious enough for the youth to appear before the Supreme Court, but I'm not going to go into detail," Mr Wurst said.
The teenager was bailed to a remote community "across the Top End" but did not have an electronic monitoring bracelet.
"One of the charges that will be considered will be in relation to the breach of bail for that particular matter," Mr Wurst said.
NT laws were tightened after a man on bail fatally stabbed bottle shop worker Declan Laverty in 2023.
"It is devastating that we are at this point again," Northern Territory Chief Minister Lia Finocchiaro posted on social media.
She later said the police presence would be ramped up after "losing yet another member of our community to crime".
"There is a family who've lost a husband, a brother, a father, an uncle, a loved one, a community who's lost a friendly face, someone they love to go and see every day," she said.
"I want to assure Territorians today that there will be very high visibility policing … particularly in retail."
The tragedy made its way into the federal election campaign.
"To see someone going to a place of work where they should feel safe and they end up being stabbed to death, that is something that is condemned by every right-thinking Australian," Opposition Leader Peter Dutton told reporters.
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