When Light's sister is kidnapped by Mellow's gang and the Kira Task Force goes to the US to do the trade for her with the Death Note, when things start getting out of control Light yells at Misa to keep writing in the Death Note.
Light: MISA! Just shut up and do like I told you, all right?! Look! I need you to keep killing Japanese criminals so just do that! This guy’s obviously investigating Kira and he won’t give up. If the killings are delayed, we are in trouble. Don’t you understand?
But as shown when L was investigating, Light focusing on an area is what lead to L's conclusion that Kira was Japanese and at this moment Light knew of Near's SPK in the US, not to mention Kira targets criminals around the world and gets a lot of the information from the internet.
Soichiro: But still, it’s impossible for us to sensor everything on the Internet. And we haven’t had any new leads in a while.
Matsuda: But posting names with faces online, I’m sorry, but if you ask me, it’s the people doing that who deserve to die. But I guess, that’s never gonna happen. Kira gets a lot of his information from the Internet so he’s not gonna kill those people.
I get why Light doesn't want the killings to die down but why is Light targeting Japanese criminals while he was in the US?
NOTE: I'm watching the English Dub released by Madman in Australia which I assume is the same Dub released by Viz Media.