An alleged plot to kill as many people as possible at a shopping centre on Valentine's Day has been foiled, say Canadian police.
A 19-year-old Canadian man and 23-year-old US woman were suspected of planning to carry out a shooting in Halifax on 14 February before committing suicide.
There could have been a "large loss of life" if the attack had gone ahead, according to authorities.
The pair had access to firearms, were apparently obsessed with death, had many photographs of mass killings, and had been on a chat site, an official said.
The woman was arrested at Halifax's airport and confessed to the plot, said the official, who added she had written a number of messages to be tweeted after her death.
The teenager had shot himself dead after police were tipped off about the plot and surrounded his home, the official went on.
Police had stopped his parents while they were driving and then officers called the suspect.
He said he did not have any guns but then took his own life as he was on his way out of the house, it is believed.
Meanwhile, a 20-year-old man was detained at the airport and a 17-year-old youth, who was wanted for threatening to carry out a gun attack at a school, was arrested elsewhere.
It is thought the pair were also involved in the plot but investigators were still trying to work out what their roles were.
The plot was not related to Islamist extremism, said authorities.
Brian Brennan, from Nova Scotia Royal Canadian Mounted Police, said: "Information gathered suggested that a 19-year-old Timberlea male and a 23-year-old Geneva, Illinois, female had access to firearms.
"And it was their intention to go to a public venue in the Halifax region on February 14 with the goal of opening fire to kill citizens and then themselves.
"Evidence also suggested that two other males, ages 20 and 17, of Halifax and Cole Harbour respectively were involved. Their role is still to be determined as part of the investigation."
He added: "Had they been able to carry out their intentions, the possibility for a large loss of life was definitely there.
"I would classify it as a group of individuals that had some beliefs and were willing to carry out violent acts against citizens. But there is nothing in the investigation to classify it as a terrorist act."