Toronto police say a mysterious tunnel discovered near a Pan Am Games venue posed no risk to the summer sporting event, but they're still seeking the public's help to find out who made it and why. 

Police held a news conference Tuesday to provide more details about the tunnel, which was first reported by CBC News. It was discovered Jan. 14 near York University's Keele Campus and the Rexall Centre, which will host the tennis events during the Games. The tunnel has since been filled in by police.

​Deputy Chief Mark Saunders said police gathered all the evidence they needed from the tunnel and sent it off to forensic investigators. Now, police are hoping to get more information from the public, specifically those who live close to the wooded area where the hole was found.

Several pieces of evidence, including a rosary with a Remembrance Day poppy affixed to it, were found in the tunnel. Police also showed off several photos of the structure — which Saunders said today measured 1.93 metres high, 86.4 centimetres wide and 10.1 metres long — as well as a secondary hole that held a generator.

Saunders said it's clear whoever built it had some level of expertise and he believes multiple people were involved given the size of the tunnel. He said for now, there's no evidence suggesting whoever who made it had criminal intentions.

"There’s no criminal offence for digging a hole," Saunders said.

CBC News has learned that police believe some of the materials used to build the tunnel were stolen from the Rexall Centre. This includes some parts of temporary bleachers used at last summer's Rogers Cup.

Police also believe that the tunnel may have been worked on as early as September of last year.

Staff Sgt. Chris Body made an appeal on Twitter for information, which was retweeted hundreds of times.

Saunders, the executive officer for security for this summer's Pan Am Games, said there is "robust security" in place for the Games and that the tunnel would have been an "eyesore" that security would have spotted. He does not believe it posed a threat to the Games.

"We'll be on top of it," Saunders said. 

With Toronto as 2015 host for the event held every four years, the Pan Am Games, one of the world’s largest international multi-sport Games, run July 10-26, followed by the Parapan American Games from Aug. 7-16.

National security officials notified

​Saunders said the tunnel case is still a Toronto police investigation, but CBC News has confirmed that national security officials have been notified.

Police have also shared pictures of the tunnel with security agencies around the world.

Ray Boisvert, CEO of risk mitigation firm ISECIS and a former assistant director of intelligence at the Canadian Security Intelligence Service, said he's concerned the tunnel was dug with "potentially malicious" goals.

"Nobody would build something like that without a specific purpose," Boisvert told CBC Radio's Metro Morning.

That purpose could be to launch an attack against York University or the Pan Am Games, he said, especially because the tunnel doesn’t seem to be the work of a survivalist or drug producer.

Toronto tunnel police pictures

Toronto police showed this image and several others of the tunnel found near York University and the Rexall Centre during a Tuesday news conference. Police are asking the public for any information they may have about the case. (Toronto Police Service)

Boisvert said police likely mounted a surveillance operation at the site, but it's possible whoever dug the hole abandoned it and went into hiding once they saw police respond to the initial discovery of it some five weeks ago.

"What worries me now is we may never know who was behind that thing," Boisvert said.

While Boisvert said the decision to call in national security officers was to guard against the "worst-case scenario," the move makes sense given the attention that will be on this summer's Pan Am Games.

"The Games are definitely in the target zone," he said.

Investigators visit nearby gas stations

CBC News has learned that investigators visited the Tennis Canada site a few weeks ago and spoke with grounds crew at that time. While investigators were on site, there was also a police presence in the woods nearby.

'Whoever decided to build this took quite a bit of time.' - Mark Saunders, Toronto police Deputy Chief

No one has come forward to claim the digging tools and generator found at the tunnel or offer any explanation for its existence.

Employees at several area gas stations were also asked if anyone had been filling up gas cans recently, in order to refuel the generator.

Saunders said it appears the tunnel was dug out by hand and the generator was likely used to power moisture-resistant lights and a sump pump that removed groundwater. He said whoever was digging was careful to conceal the tunnel and also took steps to stop any noise from coming from the generator.

Inside, the tunnel structure had plywood walls and a system of beams reinforcing the walls. 

"Whoever decided to build this took quite a bit of time," Saunders said. 

Police couldn't precisely determine when construction on the tunnel started, but said food and drink containers left behind suggest its builders spent some time there.

The rosary that was recovered from the tunnel was found hanging from a nail hammered into the wall. 

The mystery tunnel

The tunnel, marked above with a red circle, is adjacent to the Rexall Centre. (CBC)

With files from the CBC's John Lancaster