John Hinckley, the man who tried to assassinate US president Ronald Reagan 40 years ago, looks set to be granted his unconditional release from next June.

Hinckley, 66, was found not guilty on grounds of insanity of shooting Reagan and three other men outside a Washington hotel on March 30, 1981.

He said he wanted to kill Reagan to impress the actress Jodie Foster, whom he became obsessed with after watching the film "Taxi Driver."

Hinckley was released under a strict set of conditions in 2016 from a Washington psychiatric hospital where he had been held since the assassination attempt.

They included remaining within 50 miles (80 kilometers) of his mother's home in Williamsburg, Virginia, and not traveling to any area where a current or former president, vice president or member of Congress is known to be.

According to court documents, a federal judge on Monday approved an agreement between the Justice Department and Hinckley's lawyers that would lift the conditions in June 2022.

Reagan, his press secretary James Brady, a police officer and a Secret Service agent were wounded when Hinckley opened fire outside the Hilton Hotel in Washington.