NASHVILLE — He was once reported to the police in Illinois for stashing an AR-15 in the trunk of his car and then diving into a public pool wearing a women’s pink housecoat. There was the time he complained to an officer that the singer Taylor Swift had demanded a rendezvous. And then last July he was grabbed by the Secret Service when he tried to force his way on to the White House grounds.

Travis Reinking, 29, was on the radar of law enforcement well before he was taken into custody on Monday and accused of barging into a Nashville Waffle House over the weekend and opening fire, killing four and injuring four more.

Yet even after the Illinois police revoked his firearms license and ordered that his guns be transferred to his father, Mr. Reinking got them back, including the AR-15 used in the Tennessee shooting, the police said. His case raises questions over how such a troubled individual could have legally carried weapons for so long and could have continued to carry them even after he was ordered to give them up.

“We have a man who has exhibited significant instability,” acknowledged Don Aaron, a spokesman for the Metropolitan Nashville Police Department.