“That wand still isn’t working properly for you because you murdered the wrong person. Severus Snape was never the true master of the Elder Wand. He never defeated Dumbledore.”
Voldemort didn't know who was the real owner of the wand. Dumbledore had convinced Snape to kill him. Since this was arranged death, the loyalty of the wand would remain with Dumbledore. Voldemort thought killing Snape would transfer wand's loyalty to himself.
“Aren’t you listening? Snape never beat Dumbledore! Dumbledore’s death was planned between them! Dumbledore intended to die undefeated, the wand’s last true master! If all had gone as planned, the wand’s power would have died with him, because it had never been won from him!”
The new owner of the wand, did not know he had won the loyalty of the elder wand by disarming Dumbledore.
“You still don’t get it, Riddle, do you? Possessing the wand isn’t enough! Holding it, using it, doesn’t make it really yours. Didn’t you listen to Ollivander? The wand chooses the wizard. The Elder Wand recognized a new master before Dumbledore died, someone who never even laid a hand on it. The new master removed the wand from Dumbledore against his will, never realizing exactly what he had done, or that the world’s most dangerous wand had given him its allegiance
So the new owner is/was
“The true master of the Elder Wand was Draco Malfoy.”
But the new owner was disarmed (physically or without magic) by another wizard. Elder wand is power wand. It realized a changed of ownership.
“But you’re too late,” said Harry. “You’ve missed your chance. I got there first. I overpowered Draco weeks ago. I took this wand from him.”
So the new/current owner of the elder wand is:
“So it all comes down to this, doesn’t it?” whispered Harry. “Does the wand in your hand know its last master was Disarmed? Because if it does . . . I am the true master of the Elder Wand.”
The elder wand has no loyalty, it always associates itself with the more powerful wizard.
Quoting J.K. Rowling here
The Elder Wand knows no loyalty except to strength. So it's completely unsentimental. It will only go where the power is. So if you win, then you've won the wand. So you don't need to kill with it. But, as is pointed out in the books, not least by Dumbledore because it is a wand of such immense power, almost inevitably, it attracts wizards who are prepared to kill and who will kill. And also it attracts wizards like Voldemort who confuse being prepared to murder with strength.
Referred from PotterCast Interviews J.K. Rowling, part two.