Immediately, Vader steeled himself for the ruse to follow, but instead Kenobi raised his blade toward his body, closing his eyes and assuming the classic Jedi resigning stance of a sparring partner. But what might have worked as a noble gesture in the long-dead days of the Jedi Order would not save his old Master now. As Obi-Wan held his blade parallel to his frame, eyes closed, Vader could not resist the ripples of hatred and dark lust for revenge swelling in his body. He took a massive swing with his sword, cleaving the crimson blade straight throught Kenobi's Jedi robe ... striking down his former teacher with the awesome power of the dark side.
Or ... so he thought, until he recovered from the temporary blinding of his senses as the hatred overwhelmed him to find Obi-Wan's cloak dropping to the ground, flat and in a heap, with no trace of the aged Knight's body inside. Kenobi's lightsaber clanged to the ground next to his robe, and despite his heightened awareness from suspicion of another trick, Vader was still caught off-guard as he felt a surge of anguish through the Foce, accompanied by a horrified scream coming from the hangar.
He heard the stormtroopers turn and begin to fire on the escaping Rebels, and stepped forward, planting one great black boot on Kenobi's robe, unable to fathom where his body had vanished to. In that moment, Obi-Wan's words echoed in his mind "more powerful than you can possibly imagine", but before Vader could contemplate this further, a laser bolt hit nearby and his attention snapped up to the firefight occuring at point-blank range.
Three of the stormtroopers had already fallen to the floor, their white armor now tinged with black scorch marks from laser bolts. It appeared none of the Rebels had been wounded as they fled back toward the Corellian frigate, but that was per instruction once Moff Tarkin had approved Vader's plan to let them escape and lead the way to the secret base the young Princess had so fervently kept secret from them.
Even now, Vader could see the Alderaanian youth darting up the ramp of the frigate, a large brown Wookie right behind her, blaster in hand, leaving two younger men still in sight, peppering the stormtroopers with cover fire for their young Princess.
As Vader stretched out with the Force, he could feel the anguish and rage coming in waves off the younger of the two, no more than a boy really, and the Sith Lord was surprised to find the rage directed squarely at him, the anguish coming from the vision of the fallen Jedi Knight. Vader strode forward now, intrigued by this youth and his obvious emotional connection with Kenobi.
As he neared the blast door, however, the youth fired a shot directly into its control bank, activating the automatic lockdown sequence. The heavy durasteel doors spiraled together in front of Vader, cutting him off from the drama inside the hangar.