What the GI would like to lay at the Doctor's door from The Christmas Invasion is the killing of the rest of the Sycorax crew while they were retreating, but he can't, because that was Harriet Jones and Torchwood, so he has to fall back on the leader's death. The Doctor has managed to kill an awful lot of Cybermen and Daleks over the years, though.

But whereas I could identify all the Doctor's victims in the GI's second statement (eventually - it wasn't until the second watch that I remembered Solomon was David Bradley!) I couldn't place the ten billion from his opening speech, so I took it that their slaughter was the unknown and possibly future event.