Scratch broke IN TO the prison to break out Latch. The rest of the mallers come with. Scratch asks Latch if he could have done what she did to get her out. It is my belief that Scratch behaved as a cold blooded murderer to get Latch out. I think Latch is not as unstable as Scratch and may not have murder in his background.

If Scratch broke in to the prison, she probably used a fire arm. She could have gotten it from Burt's store. The story uses connection to make it more interesting. 10 million people in LA and a boy and his mom both survive 30 miles apart? Yes my pinning the safe cracking on Scratch is a stretch, but if someone else claims Burt's place was hit by the mallers, you have to get them before Burt gets there. Burt's store and the prison are on opposite sides of the LA (east / west) with ground zero in the middle and the infection wave hitting both within 30 or so minutes apart.

Last and more reaching Latch sound like the nickname for someone opens things. Later scratch gets gut and the nickname just follows. More recently we again here latch in association with a safe.