The man who shot President Ronald Reagan appeared fixated during a visit to a bookshop last year on a bookshelf bearing titles on presidential assassinations and Mr Reagan's presidency, according to testimony at a court hearing.
John Hinckley, who shot Mr Reagan in 1981 to impress actress Jodie Foster, was found not guilty by reason of insanity in the assassination attempt.
He has been held for the last three decades at a Washington psychiatric hospital, but has been granted increasing freedom in recent years as doctors say his mental illness has been in remission.
An ongoing hearing in Washington's federal court is determining whether Hinckley, 56, can begin visiting his mother in Virginia for stretches of approximately three weeks at a time, with an eventual transition to living outside the mental hospital full-time. The court case has spanned years.
The testimony from two Secret Service agents and a bookshop worker was aimed at supporting the US federal government's case that such extended visits are premature and that Hinckley remains deceptive and potentially dangerous to the community.
One agent, Jason Clinkner, said Hinckley appeared "fixated" during an October visit to a Barnes & Noble store in Williamsburg, Virginia, where his mother lives, on a bookshelf of American history books - including titles on Mr Reagan's dispute with striking air traffic controllers and the assassination of President William McKinley in 1901.
Mr Clinkner, who was conducting surveillance on Hinckley during one of his periodic visits with his mother, said he could not tell whether any particular book caught Hinckley's attention. But he said Hinckley's interest in the books, though a matter of 15 to 20 seconds, gave him "goose bumps" and was alarming given his history. "When an attempted assassin looks at a book with the cover of a person he tried to kill, it's of great concern," Mr Clinker said.
Hinckley, dressed in a blazer and buttoned-down shirt, sat impassively through the day-long hearing, occasionally whispering to his lawyers. Government lawyers have argued throughout the hearing that Hinckley is deceptive and dishonest.
Mr Reagan recovered from the shooting and went on to serve two terms as president. A secret service agent and police officer who were shot also recovered from their wounds.
Mr Reagan's press secretary, James Brady, was permanently disabled after being shot in the head outside a Washington hotel. He has since become an advocate for preventing gun violence. Mr Reagan died in 2004 at the age of 93.