Rep. John McCaherty told supporters in an e-mail not to talk about the raffle in which a .223-caliber AR-15 semi-automatic rifle is the prize, The Kansas City Star reported Thursday.
That type of weapon is the same as that used by the suspect in the Colorado movie theater shootings last Friday.
McCaherty also pledged in the e-mail not to talk to the press about the drawing.
"I have been contacted by several news sources. I am not interested in being their scapegoat. ... The less attention we give them, the quicker they move on to the next story," he said.
Tickets are $5 for the Aug. 27 drawing.
His district is on the outskirts of St. Louis.