Canadian police have foiled a plot by two suspects who were planning to kill as many people as they could in a shopping centre on Saturday.
The 19-year-old Canadian man and 23-year-old American woman planned to open fire in Halifax, Nova Scotia, before killing themselves.
Detectives said they received a tip-off after the couple discussed it on an internet chat stream.
The Royal Canadian Mounted Police surrounded the teenage suspect at his parents' home in Timberlea.
He shot himself dead after realising he was cornered.
Brian Brennan, the commanding officer of the Nova Scotia Royal Canadian Mounted Police, said officers did not believe the attack was terrorist-related, but that the suspects had access to firearms.
Timberlea is a small town on the outskirts of Halifax in the remote Atlantic province of Nova Scotia.
The female suspect, from Geneva, Illinois, was arrested at Halifax airport after getting off a flight from Chicago and confessed to the plot.
An official said the woman had planned to meet a 20-year-old man at the airport before the killings.
He was also arrested, with a 17-year-old man arrested later yesterday.
Brennan said he believed police had detained all suspects involved.
"It's a group of individuals that were of the same ... mind to commit a heinous event and then take their own lives."
He said the plot was "not culturally based", adding: "Had [the suspects] been able to carry out their intentions the possibility for a large loss of life was definitely there."
Police warned one venue of the threat, but would not say where that was, said Canadian broadcaster CBC.