I thought that Wormtail had been using Voldy’s wand? I think so anyway. That’s why his “echo” came out of the wand.

It was Voldemort's wand - used by Pettigrew - that killed Cedric. Voldemort asked for his wand back after he gained a body again ("My wand, Wormtail."). Then he used his wand to summon the other Deatheaters by pressing it against Wormtail's tattoo.

Also, it had to be Voldemort's wand that killed Cedric or Cedric's echo wouldn't have reappeared during Priori Incantatum.

Wormtail used Voldemort's wand to kill Cedric.

I'm going to go with the majority here and say that it was Voldemort's wand that killed Cedric (poor kid!) In the book, I believe it was Pettigrew who said the curse, but I have to say that in the movie (I know we're in the book forum!) it sounded a lot like Voldemort. I'm really not 100% sure though. I'm actually going to be starting a re-read of GOF at work tomorrow, so I will know in a couple of weeks!

voldemort's wand killed cedric, because then why would his soul come out during priori incantatum?
hope i helped(:

It explains it in the book. Wormtail uses his wand to kill crdric not voldemorts. then later he hands voldemort's over to him. Wormtail was to weak and cowardly to use the wand. the wand chooses the wizard and sometimes they will not work for anyone else.

It was definitely Wormtail who killed Diggory...



So we can see that Wormtail clearly killed Diggory. We also see in the films Wormtail clearly kills Diggory.
But it was using Voldemorts wand. We can see from the film that Wormtail uses a white colour wand, and the wand Voldemort uses is white, so Wormtail must have just been using Voldemorts wand. After all, if he had his own wand he would have used it to defend himself in PoA in the Shrieking Shack. So Wormtail just uses Voldemorts wand.