WASHINGTON (REUTERS) - The man who shot a presidential spokesman during a 1981 assassination attempt on Ronald Reagan will not face new murder charges, even though the victim's death last year was ruled a homicide, US prosecutors said on Friday.

Prosecutors had weighed whether to charge John Hinckley in the death of White House press secretary James Brady, who died in August aged 73, more than three decades after he was shot in the head.

Mr Brady had been gravely wounded and was left wheelchair-bound and with brain damage. The failed assassination also wounded three others, including Mr Reagan.

According to an autopsy report, a coroner ruled Mr Brady's death a homicide because his injuries made it hard for him to manage oral secretions, which in turn led to pneumonia.

Mr Hinckley, who after the shooting said he was trying to impress actress Jodie Foster and was charged with attempted assassination of the president and other crimes, was found not guilty by reason of insanity.

Now 59, Mr Hinckley has been committed for over 32 years to a Washington psychiatric hospital.

In a statement, federal prosecutors said they could not charge Mr Hinckley because a jury had already found him not guilty by reason of insanity.

Further, before 1987, Washington courts followed a "year-and-a-day rule," where a homicide prosecution could only be brought if a victim died in that time frame after an attack.

"In summary, any further prosecution of Mr Hinckley premised on his March 1981 shooting of Mr Brady would be precluded," the US Attorney's Office said.

Mr Brady was among four people shot and wounded when Mr Hinckley tried to kill the newly inaugurated president Reagan on a rainy day outside the Washington Hilton hotel on March 30, 1981.

Mr Brady spent the rest of his life working for gun control, through his Brady Campaign advocacy group he founded with his wife, Sarah.

Mr Hinckley is now allowed to leave the mental hospital to make visits to his mother's home in Virginia.