[The Dayton gunman shared a common trait with other mass shooters: misogyny.]

Separately, Mr. Kollie was accused of lying on federal firearms forms for an unrelated gun purchase and was charged late Friday with a weapons violation, the authorities said.

Mr. Kollie acknowledged that he lied about whether he was a drug user so he could receive the gun he was buying, Mr. Glassman said.

On the form, Mr. Glassman said, Mr. Kollie indicated that he was not a drug user, though he admitted using marijuana to federal law enforcement authorities in interviews after the attack in Dayton.

On the day of the shooting, officials from the F.B.I. and the Bureau of Alcohol, Tobacco, Firearms and Explosives spoke with Mr. Kollie at his home. He admitted to buying several items used by the gunman, including the body armor, an upper receiver that was attached to the AR-15-style weapon, and a 100-round double drum magazine.

The upper receiver contains the firing bolt, barrel and gas tube and is often called the “guts” of the weapon. Upper receivers and similar accessories can be bought online without background checks.