Trudeau, who was glad-handing at a Halifax mall Friday, reacted to a Federal Court decision that found fraud was involved in the robocalls.
But Judge Richard Mosley concluded in his ruling Thursday that the scale didn't justify wiping out the results of voting in six federal ridings in the 2011 election.
The ruling cleared the Conservative party and its candidates of any effort to mislead voters, though it found the most likely source of information used to make the misleading calls was the party's database.
Trudeau said the court's findings concern him.
"So the fact that there was a systematic approach to doing that is extremely, extremely worrisome," he said. "The fact that it was tied in to the Conservative database as well is an indication of tremendous concern."
The Conservatives issued a statement Thursday noting the ruling found no evidence of wrongdoing by the party or any of the candidates or campaign teams involved in the challenge. The statement also blasted the advocacy group that bankrolled the challenge.
"The Council of Canadians court challenge was a transparent attempt to overturn certified election results simply because this activist group didn't like them," the statement said.
The council paid the legal bills of the eight voters who launched the challenge and took solace in the judge's finding that fraud did occur.
"What we can do with that I think is to demonstrate that there was very shady business going on," said executive director Garry Neil.
The complainants are considering whether to appeal to the Supreme Court of Canada. If they do, the council will continue to cover the cost, Neil said.
The voters who launched the challenge were among those who say they received misleading and harassing robocalls during the campaign.
The six ridings in question are Vancouver Island North in British Columbia; Yukon; Saskatoon-Rosetown-Biggar in Saskatchewan; Elmwood-Transcona and Winnipeg South Centre in Manitoba; and Nipissing-Timiskaming in Ontario.
Elections Canada is also probing fraudulent robocalls, stemming from complaints that have surfaced in 56 ridings across the country.
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