Two people were arrested at Halifax Stanfield International Airport and have been charged with conspiracy to commit murder after an alleged plot was foiled to kill a large number of people at the Halifax Shopping Centre in the city's west end on Valentine's Day.

Lindsay Kanittha​ Souvannarath, a 23-year-old from Geneva, Ill., and Randall Steven Shepherd, 20, of Halifax have been charged.

A 17-year-old male from Cole Harbour, N.S., was originally arrested, but has since been released without charges.

Police say there is no evidence to link the teen to the charges against Souvannarath and Shepherd, but the investigation is ongoing.

Randall Steven Shepherd

Randall Steven Shepherd, also known as Randy, faces a conspiracy to commit murder charge along with American Lindsay Kanittha Souvannarath. (Facebook)

Police tracked down a 19-year-old to a home on Friday on Tiger Maple Drive in Timberlea, about 20 minutes outside Halifax. Authorities initially thought he may have been linked to the alleged plot. He was found dead early Friday, and his death is under investigation by Nova Scotia's Serious Incident Response Team.

Officers seized three long-barrelled rifles from the Timberlea home.

Souvannarath was arrested at the Halifax Stanfield International Airport after arriving in Canada early Friday, at around 2 a.m. Shepherd, who was there to meet her, was also arrested.

Brian Brennan, Nova Scotia RCMP commanding officer, said a Crime Stoppers tip from Canada helped them foil the alleged plot, but wouldn't provide more information about where they got the information.​

Mayor Mike Savage said Halifax police, RCMP, the Geneva Police Department in Illinois, the Canada Border Services Agency and the U.S. Department of Homeland Security were all involved in the operation.

Savage said people may see increased security at events Saturday, comparing it to the heightened security on Remembrance Day after the deaths in separate incidents and on different days of Cpl. Nathan Cirillo and Warrant Officer Patrice Vincent.

"Fortunately today we're talking something that could have been, not something that was," Savage said.

Neither Brennan nor Halifax Regional Police Chief Jean-Michel Blais would characterize the alleged plot as terrorism. They say their investigation shows the plan had nothing to do with ethnic or political motivation.

Brennan said the suspects "had some beliefs and were willing to carry out violent acts against citizens."

"We have averted a true tragedy here in Halifax," Justice Minister Peter MacKay told reporters. "It would have marked our city and province forever."

It appears at least one of the suspects was part of an online blogging group and the suspects likely corresponded online, MacKay said.

When asked if the suspects had "Columbine" beliefs, referring to the 1999 mass shooting at Colorado's Columbine High School, MacKay responded, "I cannot confirm that, but what I can tell you is that this appeared to be group of murderous misfits … prepared to wreak havoc and mayhem on our community."

MacKay said there is extra security at the Halifax Shopping Centre on Saturday to ensure public safety.

Privacy and police power

Savage says he has been assured that all the suspects have been caught and the threat taken down.  

Valentine's Day events, as well as the Hockey Day in Canada celebrations in Halifax, resumed as planned Saturday. People thanked officers for their efforts at the celebrations.

During his speech to reporters, MacKay said the "balance" of privacy rights and police power was on full display during this case.

"It's crucial that attacks such as this one must be prevented from happening, whenever possible. The law enforcement community must be provided with the tools they need to protect Canadians … If you commit serious crimes or plot or plan to do so, you will be apprehended and locked up for a long time."

Halifax Shopping Centre

Police say the Halifax Shopping Centre was the target of the foiled plot. (CBC)

Meanwhile, the Halifax Shopping Centre is thanking police for their efforts.

Stephanie Schnare, the marketing director, released a statement saying the mall knew early in the investigation that it was the potential target, and mall personnel have been working with officers to help out where possible.

Schnare says mall security officers have critical incidence awareness and active shooter training. Halifax Regional Police also have an office in the mall.