GOF question- who was "one more murder"?

[btk6y]

No: HPFGUIDX 32235

Question about GOF that has probably been asked before... in the first 
chapter when Voldemort is talking to Wormtail and says that they just 
need to commit "one more murder" and their path to Harry will be free, 
whose murder are they talking about?  The only person that I can think 
that he is talking about would be Crouch Sr, but he only kills him when 
he runs away from the Imperius Curse, it's not like it's a necessary 
murder.  Voldy's path to Harry would have been clear if Crouch Sr was 
alive or dead, as long as he was controlled by the Imperius curse.  
Cedric, obviously, was not who he was talking about.  Any thoughts 
would be appreciated.

Bobby