Two people have been charged in connection with a plot to carry out a mass shooting in Halifax, Nova Scotia, Canadian police say.
Police said Lindsay Kantha Souvannarath, 23, and Randall Steven Shepherd, 20, are due to appear in court on Tuesday.
A third person has been released without charge.
Media reports say a 19-year-old man found dead had written a blog with dark references to death and shootings.
The man, identified as James Gamble, posted a picture of himself holding a rifle and a knife.
"Valentine's Day it's going down," he is quoted as writing by CBC News.
"What doesn't kill me might make me kill you," he also reportedly writes.
Police say they unearthed the plot following a tip-off from Crime Stoppers on Friday - just a day before the plan for a shooting spree in the Halifax Shopping Centre had allegedly been due to take place.
Justice Minister Peter MacKay said if it had gone ahead it would have "been devastating, mass casualties would have been a real possibility".
But all suspects are now either dead or in custody, he said.
Ms Souvannarath and Mr Shepherd were arrested at Halifax airport after Ms Souvannarath arrived on a flight from her home state of Illinois, the US, police said.
The pair have now been charged with conspiracy to commit murder.
Police found the man named as James Gamble dead at a house in Timberlea outside Halifax after they arrived and surrounded it. They have refused to confirm reports that he shot himself.
They found three long-barrelled rifles at the address, said Nova Scotia RCMP commanding officer Brian Brennan.
Another man has been questioned and released without charge.
Among the dark references in Mr Gamble's alleged blog uncovered by CBC are references to the 1999 Columbine high school massacre in Colorado, the US, and to Adolf Hitler and the Nazis, the news organisation reported.
Police say the attack was not related to "ethnic or political considerations" and was not terrorist in nature, but have not speculated on the motivation for the alleged plot.