Matt Campbell, whose brother Geoff died in the 9/11 attacks, has spent two decades pursuing what he believes is proof that the destruction of the World Trade Center was not solely the result of the terrorist hijackings but part of a wider cover-up. He argues that no one has ever been held properly accountable for the deaths of nearly 3,000 victims, and he rejects the "conspiracy theory" label, insisting his position is based on unresolved evidence rather than idle speculation. His campaign matters because it reflects a persistent, and in some quarters growing, body of alternative theories about the attacks a quarter of a century on.

Campbell, a reflexologist from Brighton, believes incendiary devices rather than the hijacked aircraft brought down the Twin Towers and World Trade Center 7, and suspects US government or intelligence involvement, though he stops short of naming those responsible. This week he is due to speak at a New York conference, "Turning the Tide: 9/11 25 Years Later," alongside around 40 other speakers including first responders, and next month he plans to attend a London Supreme Court hearing linked to his campaign for justice. The article also notes other long-running alternative theories, including claims involving Mossad or that the Pentagon was hit by a missile, and cites architect Richard Gage, a prominent advocate of the "controlled demolition" theory, who says he has been taken more seriously in recent years, including by commentator Tucker Carlson.