Border officials who confiscated a British man's ashes at St. John's International Airport earlier this month likely had "probable grounds" to believe the man was carrying a narcotic, Canada Border Services Agency says.

In a statement to CBC News, a representative with CBSA's Atlantic region would not comment on the specifics of Russell Laight's case.

Laight was flying to Halifax from England on March 2 when his plane was diverted to the Newfoundland airport due to poor weather.

According to Laight, border agents tested the ashes of his deceased friend, which Laight was carrying in his bag, and found traces of the anaesthetic drug ketamine.

Russell Laight was held in the St. John's jail for five nights after border officials mistakenly detected traces of an illegal drug in the ashes of his deceased friend. (Steve Berry/CBC)

Laight was taken into custody and held for five nights in the St. John's lockup. Further testing in Montreal confirmed that the ashes did not, in fact, contain ketamine.

CBSA said it's "unable to provide an interview at this time," but did comment on border inspections.

"Secondary inspections are a part of the normal cross-border travel process and border services officers are trained to perform these examinations in a courteous, respectful and professional manner," read the statement.

The ashes contain the remains of Simon Darby, who passed away from cancer in December of 2015. Darby requested his ashes be spread in Atlantic Canada. (Tracey Jonasson)

The CBSA said detection technology, like the narcotic identification kit test used to test the ashes carried by Laight, "will from time to time produce a false positive." But according to CBSA, false positives occur "less than one per cent of the time."

"If field tests return a positive result then CBSA officers have probable grounds to suspect the substance is a narcotic and the material is seized, the traveller is subject to detention and afforded their rights," the agency said.

From there, the agency notifies the Combined Forces Special Enforcement Unit-Newfoundland and Labrador and an investigation begins.

According to the CFSEU-NL, Laight "at no point during the arrest provided any explanation to authorities that the substance was human remains."

In a statement to CBC News, the unit said additional testing was done and the matter was "immediately addressed" once officials became aware of the ashes on Friday.

"The charges were withdrawn and the traveller was released on Monday once the results were received," the statement read.

The ashes have not yet been returned to Laight. The CBSA is expected to receive the remains on Monday or Tuesday, and will subsequently give the ashes back to him.