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... A host of basic questions remains unanswered four years later. For starters, investigators haven't determined if the suspect is a man or a woman. Nor have they established a clear link between the pipe bombs and the Jan. 6, 2021, riot at the Capitol by a mob of Donald Trump's supporters.

The FBI "can't work on assumptions," said David Sundberg, assistant director in charge of the bureau's Washington field office.

"Without being able to confirm the suspect's identity, it is very hard to definitively establish motive," Sundberg told The Associated Press. "Therefore, it would be difficult for us to state that there is a link, although we can't state there is not one." ...