Ottawa Police said initial X-rays of the package showed what appeared to be wires, batteries and a dense material that could have been components for an improvised explosive device.
But sources close to the investigation say that when police destroyed the package to disable its potentially dangerous contents, they found no explosives or bomb-like devices.
RCMP are still investigating the case to determine who sent the mysterious package to National Defence and why.
It's unclear what exactly was in the package, but the source said it did not appear to have been left by accident.
"This wasn't someone's iPod, headphones and a sandwich that fell off someone's bike going past DND," said one source familiar with the probe.
The police response at 101 Colonel By Dr. at about 3:15 ET Tuesday afternoon forced the shutdown of Mackenzie King Bridge heading into the rush hour, causing major traffic disruptions in downtown Ottawa.
The north tower of the building was evacuated not long after the package was found at the north entrance.
A chemical, biological, radiological, nuclear and explosives team (composed of Ottawa police and RCMP) attended the scene, along with military police.
X-ray scans reveal possible explosives, power source, wires
A robot was used to remove the package from the building and X-ray it.
The scans revealed dense material that could have been explosives, according to Ottawa police Insp. Michael Maloney, as well as something that looked like it could have been a power source.
The scans also showed wires that could have connected the other materials.
"From what they ascertained off of the X-ray, they determined that there were components that were consistent with what you would require for an improvised explosive device," he said Wednesday morning.
"That doesn't mean that there were actual explosives, but there were components that were consistent with what is required to make a bomb."
Water blasts used on package
Police used a high-velocity water cannon to "disrupt" the package for further investigation, Maloney said. When that failed, police used what's called a water bottle charge — which contains a small amount of explosive — to blast the package and make it safe.
No one was hurt, and Maloney said there was never a threat to public safety.
A joint investigation by Ottawa police, RCMP and the Department of National Defence is ongoing.
Defence Minister Peter MacKay said he's working closely with law enforcement to learn more about the incident.
"I don't want to get into speculation until we get a full picture on what this package was and what was behind it," he told reporters Wednesday.
"I can't say enough about the reaction time of members of the Canadian Forces and the Ottawa city police who we worked very closely with. The building was evacuated, precautions were taken as they would be in all cases, and the item, the package, was removed and detonated."
Public Safety Minister Vic Toews said Canada's security agencies are "very vigilant" in trying to find possible dangers.
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