CALGARY - Cops investigating death threats against Immigration Minister Jason Kenney breached a suspected impaired driver's Charter rights when they "boxed" him in, a judge has ruled.

In a written decision released Friday, provincial court Judge Allan Fradsham said police "arbitrarily" detained Joseph Reid, when they pulled up behind him in a strip mall.

Fradsham said had the cops pulled up beside Reid's SUV during their Jan. 28, 2010 investigation, they would have been entitled to question Reid about his suspicious behaviour.

But Fradsham agreed with defence counsel Greg Dunn the officers unjustly detained Reid by blocking his escape when they had no reasonable grounds to do so.

Crown attorney Jonathan Hak argued Reid's suspicious behaviour -- quickly pulling into a parking stall and shutting off his engine when spotted by the officers around 3:30 a.m. in a deserted parking lot -- warranted further investigation.

"The police would not be doing their job if they noted these ... factors and said, ‘Well, that's interesting, let's go get a coffee,'" Hak submitted.

But Fradsham said the officers went too far when the boxed in Reid's vehicle when they pulled up directly behind him to prevent any escape.

"Available to the officers in the proper performance of their duties was an acceptable middle ground between violating the accused's ... Charter rights and simply deciding to ‘go get a coffee,'" Fradsham said.

"The mere suspicion harboured by the officers justified them asking the accused questions, but it did not justify detaining the accused for investigative purposes," he said.

The officers were in the area because it was near Kenney's constituency office and the minister had received a death threat three days earlier.

Fradsham must still hear arguments from Dunn and Hak as to whether excluding the evidence police subsequently obtained from Reid, two breath samples, would discredit the administration of justice.