Former Manitoba RCMP officer Gordon Kowalchuk said he watched in horror as events in Moncton unfolded.
RCMP and other police agencies locked down the city of Moncton as the search for the killer continued.
The suspect was apprehended early Friday morning.
Police had asked Moncton residents to keep their outdoor lights on to facilitate their search.
Kowalchuk is asking Canadians to turn on their outdoor lights and keep them on, until the three fallen officers have been laid to rest.
He said when RCMP asked people to keep their porch lights on during the manhunt, he saw it as a symbol of hope.
"Bad guys hide out in the darkness," he said. "So for me, the lights in Moncton were hope."
He said it's also a recognition of what police do.
"It's saying to the guys that are patrolling down your street, 'Yeah, there's a light on. There's safety in us," he said.
It would also send a message to officers on the job.
"It's important because at times like this, [because] a lot of police officers question their calling," he said. "I asked myself at the time of Dennis Strongquill and Mayerthorpe incidents. Am I doing the right thing? Why am I doing this?"
Since the shootings in Moncton, people have been tweeting images from around the world of lights left on in support.
Kowalchuk's neighbour, Lesley Shepherd, is also looking for a way to express her shock and sorrow after the deadly violence in Moncton.
"I have no words. I just ... It's gone beyond words, I think, at this point," she said.
Shepherd said she'll be keeping her porch lights on, for sure.
"I'd do anything I can," she said. "And his idea was just very simple, ... making the statement, 'Yes, we're here and we're supporting you and you are not alone.'"
Across the street, Ed Tymofichuk's lights are also on, even though it's the middle of the day.
"It's a way of showing we care and we do care about the families and what happened and expressing hope for the future that these things won't repeat themselves," he said.
Kowalchuk summed it up this way: "It's just a way of saying we honour you. Thank you. And come home safe tonight."