"We can confirm that none of the envelopes contained a noxious product of any kind," provincial police spokesman Richard Gagne said in a phone interview.
Authorities know what the substance is but won't reveal that for now because it's an important element in their investigation, he added.
"The exact nature of the product will be disclosed once the investigation is completed."
Gagne also hinted that the same people may have been responsible for all four envelopes.
"It's logical to believe it would have been the same person or persons...but for the moment we don't have the proof to make a judgment beyond all reasonable doubt," he said.
The envelopes were discovered Thursday in the riding offices of Denis Lebel, the Conservative minister responsible for Quebec, and three other cabinet ministers — Christian Paradis, Maxime Bernier and Steven Blaney.
Certain media reported the envelope sent to Lebel's office included a warning the Conservatives would be "annihilated."
Lebel confirmed Thursday the envelope at his office in Roberval contained a note but said he did not know what was written.
"We won't be intimidated," he added.
The only other Conservative MP in Quebec, Jacques Gourde, did not receive any such mail.
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