The group behind an ad campaign questioning the official explanation of 9/11, which is running on [municipal buses in Ottawa], says its message should be protected as free speech. The group called Architects & Engineers for 9/11 Truth have launched a global ad campaign called "ReThink911," which is running in other cities including New York and Toronto. The campaign takes aim at the U.S. government's explanation that World Trade Centre 7 - the "third tower" - fell as the result of fire. Carleton University student Andres Acero first spotted one of the group's ads aboard an OC Transpo bus earlier this week. A volunteer with a campus first responders group, Acero said he thinks the ads are disrespectful to the first responders who lost their lives during the 9/11 terrorist attack. Transit commission chairwoman Diane Deans agreed, saying while it was a "difficult challenge" to balance the constitutional right to free speech with community acceptability, she thought the ads were "insensitive." Architects & Engineers for 9/11 Truth responded, taking issue with the notion they were being insensitive to run the campaign. They also said their campaign is sponsored by a group representing more than 100 victims' family members. "To Councillor Deans and to all who question our sensitivity and legal right to run the ReThink911 ads, we would like to make clear: the ReThink911 coalition includes 9/11 victims' family members who want nothing more than an accurate and unbiased accounting of the death of their loved ones," the group said in a letter published on their website.