The problem with this scenario was that Hitler had seriously beefed up his security detail in the wake of Stalingrad. Not only were there far more SS security troops, but officers also had to surrender their sidearms. These men had to check their weapons before meeting Hitler, which rankled more than a few officers. There were also rumors that Hitler himself wore a bullet-proof tunic as well as lining his hat with armor. Some of the conspirators did think of shooting Hitler. The security detail was not airtight enough to prevent a smuggled pistol. Lieutenant-Colonel Georg Freiherr von Boeselager was at one point considered to be a candidate by the conspirators for a pistol assassination despite the assassin's reluctance to shoot a man in cold blood. There was a plan to shoot the dictator when he visited Army Group Center, but the plotters could not go through with it in March 1943. The reasons for the failure of the March attempt are still unclear. Ian Kershaw's Hitler biography notes that Hitler's erratic itinerary made it difficult to carry the attempt out but also these military men feared wounding fellow officers. Peter Hoffman's study of the resistance contends that the plotters lost their nerve given Hitler's omnipresent security detail and that if these men were caught with a weapon it risked giving up the whole conspiracy. Eventually Rittmeister Eberhard von Breitenbuch volunteered to shoot Hitler with a smuggled Browning pistol. von Breitenbuch made an abortive attempt to kill Hitler via a pistol 11 March 1944 when he visited the Berghof, but Hitler's security detail elected not to allow aides to attend a conference with Hitler. These failures underscored to Tresckow and other plotters the superiority of bombs over firearms. An explosive device would be much less conspicuous than a smuggled firearm and could hide among an officer's baggage. A random search could overlook an explosive device while a pistol was another matter entirely. By the same token, explosives negated possibility of Hitler's increased SS security detail interfering with the assassination attempt.