MONTREAL - Montreal police have stepped up patrols in the metro system Friday.

Co-ordinated smoke-bomb attacks crippled Montreal's subway system yesterday, snarling the morning commute for thousands of people.

Police quickly released pictures of four suspects after devices were set off at multiple points during rush hour.

Many angry commuters condemned striking students, but student protest leaders pinned it on rogue troublemakers.

Some even suggested the fault actually lay with Premier Jean Charest, for not bending to the protesters' demands.

It wasn't the first subway interruption Montreal has experienced in recent weeks, as the city has dealt with some unwieldy student demonstrations.

Police are looking for four suspects -- a man and three women -- all believed to be in their 20's.

They've warned in recent week that some radical groups have been taking advantage of students' anti-tuition battle to create their own damage.

Several suspects identified

Metro riders were quick to provide police with photos of three women and one man, all believed to be in their mid-twenties, suspected of throwing smoke bombs at the Lionel-Groulx metro station.

They are described as a white woman wearing a black sweater and tights, with a pale grey skirt, wearing a beige shoulder bag and brown sandals. She has dark hair that was in a pony tail.

The second female suspect was wearing a dark brown or black shirt over a green shirt, a purple scarf, blue jeans and eyeglasses. She has wavy hair that was tied back in a bun, and was carrying a brown leather purse. She may have been wearing white sneakers.

The third female suspect had black tights over a black skirt or dress, and was wearing a green baggy sweatshirt, possibly hooded. She was carrying a black shoulder bag.

The male suspect was wearing a grey and black striped poncho-style knit sweater over an orange or red shirt. He has longish blond hair and was wearing dark jeans.

The clearest of the photos were taken furtively by a commuter who grew suspicious when he allegedly saw the three women force open a metro door and toss something outside onto the tracks.

Anyone with information is asked to call Info-Crime at 514-393-1133.

Hours of disruption

By 8:50 a.m. the STM was forced to close the entire underground network, including the Yellow line.

Partial service resumed along the Orange and Green lines 20 minutes later, only for the STM to announce yet another stoppage at 9:30.

By 9:40 only the Yellow line was operational. The Blue line and Orange lines were running smoothly again at 10:10, while only at 10:40 a.m. was the Green line open for its entire length.

The STM rearranged the buses available to ferry commuters around the city, but with multiple lines down there was no hope of a smooth, easy commute for hundreds of thousands of people.

Meanwhile Laval's transit system pushed buses into action to bring people to the Henri Bourassa station, while the Longueuil transit system added buses to bring commuters to the Papineau station.

Montreal's bicycle-sharing service Bixi rolled into action as well by opening several drop-off and pickup depots in downtown Montreal with far more bikes available than usual.

Two stations were set up at the intersection of King and De la Commune Sts, and St. Alexandre and Ste. Catherine Sts. Two more depots opened later at Square Victoria and Place D'armes, and another three at major intersections along de Maisonneuve.

Many people hearing about the attack decided to drive to work instead, and streets throughout Montreal were bumper-to-bumper with car traffic.

Commuters displeased

The incident was a bummer for those forced to scramble for alternate commuting plans on the gloomy morning chill.

"Yeah, it was pretty terrible. C'etait vraiment horrible," said one. "I heard that there was some fume bombs and stuff and I am just going to walk my way to work today."

Another employed technology to cope with the subway snafu.

"I just looked on the website on my phone and was able to find out that everything was shut down so, after that it was trying to find manage my way across the city," said another.

Another waited it out for 45 minutes.

"I was actually stuck at Place des Arts metro station and just waited around the metro waited for things to get back on."

Multiple attacks in past few weeks

Several times over the past four weeks the metro has been targeted by people using smoke bombs to disrupt service.

On April 16, 2012, bags of bricks were thrown onto the tracks at several stations and emergency brakes were pulled on multiple lines.

Police have identified five suspects in that co-ordinated attacks, visible here, and are asking for help in identifying the culprits.

Charest, Tremblay condemn attacks

Mayor Gerald Tremblay asked Montrealers to "take back their city" following the incident.

"No cause, legitimate or not, can justify any criminal action that jeopardizes public security," said Tremblay during a heated press conference.

Quebec Premier Jean Charest also condemned the attack.

"It's inexplicable," Charest told reporters in Gatineau, Que. "There's no reason to commit acts of intimidation and violence. There's no excuse for this -- none."

Charest made an effort to avoid jumping to the tempting conclusion that the attack was organized by tuition protesters.

"Hopefully we'll find the culprits. They are responsible for what they do, any other allusion is totally wrong," said Charest.

Other Liberal cabinet ministers also weighed in on the attacks.

"It is a shame that people are doing such acts because obviously it causes damage to people who are not involved. I think it is against the most basic social behaviour," said Transport Minister Pierre Moreau.

"We have to have the collaboration of everybody," said Public Security Minister Robert Dutil. "It seems that it's a concerted movement in Montreal."