The city of Kelowna, B.C., has wrapped up its investigation into the mysterious disappearance of several atheist bus ads, but staff are no closer to knowing what happened to the controversial signs.

The ads, which question the existence of God, were removed from the sides of two city buses on April 29, two weeks into the one month paid for by advertisers. Several drivers refused to drive the buses because of the two-and-a-half by 11.5 foot ads, which read "There is probably no God – now stop worrying and enjoy your life."

The campaign was paid for by the Centre for Inquiry Canada, a skeptic group that has sponsored similar campaigns on transit across the country since 2009. The ads were up for only two weeks of the month paid for the CFI.

Regional programs manager Jerry Dombrowski says the results of the review are inconclusive.

Dombrowski said the investigation found no evidence of unauthorized entry into the BC Transit yard where the buses were sitting.

But he said the decals aren't difficult to remove and staff aren't even sure if the buses were in the transit yard or kept off-site.

"With no witnesses or video surveillance to go on, how and when the advertisements were removed remains unknown," Dombrowski said.

The CFI believes the ads were taken down by a professional because there was no trace of residue left on the buses.

CFI Canada Executive Director Justin Trottier feels that he has been intentionally been left in the dark about what happened to their ads, which were slated to remain on the buses until Wednesday.

He said both the City of Kelowna and BC Transit have refused to correspond with him about the disappearance.

"The process has been horrendous and the lack of respect for our speech rights is astounding. We are paying customers," Trottier told in a telephone interview.

Several transit companies across Canada, including BC Transit, have refused to run their ads in the past, citing policies against provocative or ideological messages.

But the CFI's ads have been approved by the Canadian Standards Association, and many transit providers have since relented – including in Vancouver and Victoria, where the campaign may be heading in the near-future.

"We fought for two years to get these ads up and then they come down. It's very unprofessional. One way or another we'll finish the campaign," Trottier said.

CFI Canada is asking for an apology from the City of Kelowna, as well as a reimbursement to cover the costs of reprinting.

While similar CFI ads have been the victim of graffiti in the past, the organization said the Kelowna incident is unprecedented.

A similar ad campaign was rolled out with some controversy on more than 200 buses in Britain in 2009.

Organizers said the Atheist Bus Campaign was intended to place "peaceful and upbeat" messages about atheism on public transportation in response to Christian advertising.