KEARNEY, Mo. - A fiery explosion that left outlaw Jesse James' half-brother dead and maimed his mother was part of a conspiracy by lawmen to kill the bandit, a new documentary alleges.  It had been dismissed for more than a century as an accident.

    Instead of stopping the James gang's robberies of railroads and banks, the bombing drove its embittered leader's criminal career and won him public sympathy, according to the documentary, "The Life and Death of Jesse James."

    The film blames the Jan. 26, 1875, bombing on frustrated officers of the Pinkerton National Detective Agency, whom James' band of former Confederate guerillas had eluded for years.

    Historians say James wasn't around when the explosion ripped through his family's log farmhouse, dubbed "Castle James" by the bandit's enemies.  It killed 8-year-old Archie Samuel and forced the amputation of part of the right arm of Zerelda Samuel.

    It also prompted an unsuccessful push in the Missouri Legislature to grant amnesty to the James gang.  One state representative, a former Union soldier, called the blast "the most cowardly and brutal outrage ever committed in the state."

    Cited in the documentary is a letter discovered recently in the National Archives among late-1800s papers of Allan Pinkerton, head of the detective agency and founder of the U. S. Secret Service.  His company, which once guarded Abraham Lincoln, was working for robbery-plagued railroads and banks.

    The letter, handwritten a month before the explosion, was addressed to lawyer Samuel Hardwicke of Liberty, a local contact for Pinkerton.  Although parts of the letter are illegible, the documentary says Pinkerton gave Hardwicke detailed instructions for a raid on the James family farm in the rolling hills outside Kearney.

    At one point, the film says, Pinkerton told Hardwicke: "Above everything destroy the house...Let the men take no risk, burn the house down."

    Pinkerton also told Hardwicke to have the raiders use "Greek fire," a primitive type of bomb.  Two explosive devices were hurled into the farmhouse, historians say, but it has been long assumed they were to illuminate the inside of the darkened building, not destroy it.

    "This is the first conclusive evidence that the Pinkertons conspired and then set off  the explosion," said documentary producer Ron Casteel, a former radio and television newsman in Los Angeles and San Francisco.  "It shows planning and execution of a callous and deadly act."