Voldemort's 8th Horcrux

[greg_a126]

No: HPFGUIDX 137530

So we know that Voldemort was obsessed with the idea of having 7 
Horcruxes, b/c 7 is a magically strong number.  We all now know, that 
he only has 5.  We also know that he knows the diary has been 
destroyed, so he thinks he only has 6.

The reason that Slughorn seems amazed that young Tom Riddle is even 
thinking about having that many is b/c to have that many, you'd have to 
kill that many people.  Based on the blase way that he has Wormtail 
kill Cedric in GoF ("Kill the spare"), he doesn't put any more thought 
into it than most people would about brushing their teeth.  

All that being said, what't to keep Voldemort from creating an 
additional Horcrux in order to keep it at the magically strong number 
7.  Amelia Bones was a very powerful witch that Dumbledore was upset  
about losing.  Why couldn't Voldemort have used this murder to get his 
number of Horcruxes back up to the magically strong number of 7?

Greg