terrorist talk. he says he saw thousands of people celebrating in new jersey after the 9/11 attacks. >> i watched in new jersey where thousands and thousands of people were cheering as that building was coming down. >> reporter: standing by his claim, even as news organizations and government leaders call it false. >> you know, the police say that didn't happen. >> people that were cheering on the other side of new jersey where you have large arab populations, they were cheering as the world trade center came down. >> reporter: tonight, trump is not backing down, even asking "the washington post" for an apology. the billionaire is pointing to this sentence in "the washington post" a week after attacks. law enforcement detained people after cheering on rooftops in new jersey city. cnn has found no evidence of arrests or a video shows muslims