The memo was obtained Thursday by The Oregonian/OregonLive and a defense lawyer for Cliven Bundy now wants federal charges against his client dismissed.
The trial is currently underway in Las Vegas.
BLM investigator Larry Wooten alleges supervisory agents didn't turn over required evidence to the prosecution team.
He also says they mocked the Bundys and their followers and were too heavy-handed as they engaged with armed ranchers.
The standoff stopped a government cattle roundup three years ago in Nevada.
The defendants face 15 felony charges including assault and threats against federal officers, obstruction and extortion.