Quebec police say the white powder found in envelopes sent to the riding offices of the four federal cabinet ministers from the province was harmless.
Provincial police spokesman Richard Gagné says none of the four envelopes contained a noxious product of any kind.
He says authorities know what the substance is but won't reveal that for now because it's an important element in their investigation.
Gagné also said in an interview on Friday that it's believed the same person or persons were responsible.
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.
The only other Conservative MP in Quebec, Jacques Gourde, did not receive any such mail.