Two phones and at least one other device were severely damaged, as if to hinder recovery of their contents, including one that was so badly smashed that it has slowed efforts to extract information, the officials said.

A cellphone Ms. Malik had with her on Wednesday had almost nothing on it — no social media apps or encrypted apps — prompting investigators to suspect that it might have been a “burner phone,” meant to be used and discarded.

Asked if the design of the explosive devices had come from Inspire, an online magazine published by an arm of Al Qaeda, Mr. Bowdich said investigators were looking into that possibility.

Two senior United States security officials said that F.B.I. counterterrorism officials were overseeing the investigation because of the possibility that it might be terrorism, not because they had concluded that it was.