A friend of the man who shot nine people dead in the Dayton, Ohio, massacre told investigators that he bought the body armor and ammunition the gunman used in the attack, the authorities said Monday.

Ethan Kollie, 24, bought the items for the gunman, Connor Betts, and then kept them in his apartment to help Mr. Betts hide them from his parents, said Benjamin C. Glassman, the United States attorney for the Southern District of Ohio.

There was no evidence that Mr. Kollie intentionally helped in the planning of the attack, Mr. Glassman added. Mr. Betts was killed in the shooting.

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 following the shooting on Aug. 4.

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 body armor and a gun accessory.

Officers interviewed him again on Aug. 8, and they said Mr. Kollie told them he had done hard drugs with Mr. Betts four or five times a week in 2014 and 2015.

After officials got a federal search warrant, he again admitted to being a regular user of marijuana and psychedelic mushrooms and to growing them in his residence.