A medical examiner ruled Brady's death last year a homicide, finding his death was a result of the wounds he sustained when he was shot in 1981 during an attempt to assassinate President Ronald Reagan. But the office of the U.S. attorney for Washington said it had decided against charging Hinckley with the crime.
"The decision was made following a review of applicable law, the history of the case, and the circumstances of Mr. Brady's death, including recently finalized autopsy findings," a statement said.
Hinckley, now 59, said he tried to kill Reagan because he was infatuated with the actress Jodie Foster. He was found not guilty by reason of insanity and has spent his life since then in St. Elizabeth's Hopital in Washington.
Brady sustained devastating injuries in the shooting, which occurred just over two months after Reagan became president. He was partly paralyzed and, for the rest of his life, used a wheelchair, but he survived for 33 years, dying in August at 73.
He went on to become an advocate for gun control.
Ted Williams, a defense lawyer, told WRC-TV that prosecuting Hinckley would have been difficult because there is no evidence that was not presented at Hinckley's trial in 1982. As an additional complication, Washington had a rule at the time that murder prosecutions could only occur if the victim died within a year and a day of being injured.
Hinckley has been allowed greater freedom over the years. He can now spent up to 17 days each month with his mother in Williamsburg, Va., although his movements there are strictly controlled.