A convicted murderer scheduled to die tonight by lethal injection asked a federal judge this afternoon to stop the execution. Karl Roberts had not yet taken his case to federal court. His lawyer, Craig Lambert, made the motion five hours before a scheduled double execution. Lambert did not immediately return calls for comment. Roberts filed a request for a stay of execution with US District Judge George Howard Junior in Little Rock. Attorney General Mike Beebe`s office filed papers opposing Roberts` request and asked that the execution go forward. No word yet from Howard`s office.