They paid $2,000 US to cross B.C.'s border with Washington state.

And they would have owed a smuggler another $11,500 US once they reached their destination.

Instead, the group of 10 Mexicans — including two children — were caught by U.S. border patrol agents in the back of a white van about five kilometres south of the Canadian border the day after they made their late-night crossing last May.

In a search warrant sworn to obtain phone records, U.S. authorities now allege a Canadian permanent resident is part of a group smuggling Mexican nationals into the U.S. from B.C., and from Alberta into Montana and eventually on to Texas.

The warrant was filed last week in U.S. District Court for the District of Montana.

According to a spokesperson for U.S. Customs and Border Protection (CBP), the document would normally have been sealed, as the investigation is ongoing, but appears to have been made public in error.

Regardless, the document names several people — including a resident of Canada and a visitor to Canada — who are suspected in four separate illegal border crossings involving more than two dozen migrants.

'One of them had two young children'

CBC is not naming the individuals under investigation, as none of them has been charged. They are identified by initials for the purpose of this story.

They could not be reached for comment and the search warrant does not give any details of their whereabouts.

But, according to the documents, border patrol investigator Shane Rice says he obtained a phone belonging to the Canadian resident.

U.S. Customs and Border Protection is tasked with monitoring both the southern and the northern border for migrants crossing into the country illegally. (Loren Elliott/Reuters)

"Instant messages sent and received during the smuggling event were discovered stored within the telephone," Rice writes in the application to obtain the warrant.

"These messages talk about ... the difficulty crossing the border due to the number of Border Patrol vehicles on the road and the inability to move quickly because one of the smuggled persons had a bad leg and one of them had two young children."

The warrant is for information contained on the phone of another of the suspects.

Heightened security on the U.S. border with Mexico under the administration of President Donald Trump has led American law enforcement officials to warn about the vulnerability of the northern border.

"At 5,500 miles in length, the northern border of the United States stands as the longest common border in the world," CBP spokesperson Jason Givens said in an email.

"As America's frontline border agency, CBP is responsible for securing America's borders against threats, while facilitating legitimate travel and trade."

The heightened focus on migrants at the southern border has led U.S. law enforcement officials to now focus on attempts to bring Mexican citizens into the U.S. through Canada. (Christian Torres/The Associated Press)

U.S. border patrol statistics show an increase in apprehensions of migrants crossing the northern border illegally from 3,230 in 2013 to 4,316 in 2018.

During the same period, the number of apprehensions at the U.S. border with Mexico dropped from 414,397 in 2013 to 396,579 in 2018.

Overall, the numbers show a gradual decline in the number of apprehensions over the past two decades: there were 12,108 apprehensions at the northern border in 2000 and more than 1.6 million people caught at the southern border the same year.

Identified as 'foot-guide'

The investigation detailed in the search warrant begins in August 2018 with a traffic stop of a U.S. citizen in Texas — identified here as MG — who was found to be transporting Mexicans from Montana to Houston.

A month later, MG was stopped in Montana in the hours after surveillance cameras recorded an alleged associate walking north from the U.S. into Canada.

The same associate was identified in surveillance footage on May 1, 2019. But the warrant says he was now acting as the "foot-guide" for a group of 12 people travelling in the opposite direction — into the U.S. from southwestern Alberta.

"The foot-guide will commonly be found in the front of the group to lead and set a travelling pace for the group," Rice writes.

"I know that at night, groups will form a single file line and follow the exact path of the foot guide."

Ten days later, cameras recorded the crossing of another group of people into Washington, where they were apprehended.

Rice says agents also stopped MG driving a pickup the same night.

He "claimed to be lost and on a road trip from New Mexico," the documents say. The agents released MG, but later learned that he was a suspect in the earlier human smuggling cases.

'Rekindle the flame'

At roughly the same time, Canadian police stopped two vehicles north of the border. One was driven by ER, a Mexican citizen in Canada as a visitor, and the other by EP, a Mexican citizen in Canada as a permanent resident.

According to Rice, EP's sister had once been married to MG.

EP "admitted to dropping off the group to enter into the United States," the warrant says.

A month later, EP was also allegedly photographed crossing the border illegally back into Alberta a day after RCMP equipment recorded a group of four to six migrants going in the opposite direction.

According to the warrant, evidence shows the same group of alleged smugglers were linked to a September 2019 border crossing of six to eight people in southwestern Alberta.

In the hours after the group crossed into Montana, MG was stopped in the area by border agents who questioned and released him. MG said he was camping nearby with EG's sister — his ex-wife.

He told investigators the pair were trying to "rekindle the flame."

No charges have been filed against any of the suspects. RCMP did not respond to a call for comment. Givens said the investigation in the U.S. is ongoing.