A U.S.-based 911 expert is weighing in on the controversy around a cancelled emergency call minutes before a fatal shooting last weekend in Winnipeg.

Rustom Vito Paclipan, 23, was killed early Sunday outside the Opera nightclub on Main Street. Winnipeg's police chief has called for an internal investigation into why the original 911 call about a fight was cancelled, and has put the staff involved on administrative leave.

Less than four minutes after the call was cancelled, Paclipan was shot dead.

Paul Linnee, a 911 expert from Minnesota, said fight calls are considered high priority in the United States and aren't likely to be cancelled.

While he can't speak specifically for the Winnipeg dispatchers, he said 911 operators can get mixed messages from multiple callers about the same incident.

"You really ought to be cautious about ever cancelling their response, based on information form party A, party B, party C or whoever else, even if the original caller calls you back and tells you don't have to come," said Linee, a certified ENP (Emergency Number Professional) who describes his specialty as "analysis and reconstruction of 911 dispatching events and allegations of them being mishandled."

One of those parties, responsible for attacking the other, could be trying to cancel someone else's emergency call, he said.

"The decision to revoke that [emergency] response has to be taken with considerable care because there's any number of people out there, who for whatever their personal reasons might be, might not want the cops to come," Linee said.  

Winnipeg police have said the 911 call was cancelled from within the 911 Communication Centre. It is not known why that decision was made — whether a call came in saying it was no longer necessary.

Operators must always be suspicious of someone calling to cancel any 911 call, he said.

You can listen to his full interview with CBC Information Radio host Marcy Markusa — and why he believes police shouldn't be the ones investigating the incident — by clicking the audio link at the left of this page.