I have a really serious doubt. I am from Spain, and I read the whole series in an edition published by a publisher called Planeta Comics. This chapter is slightly different from other versions of it I found online. In the version I read after Kenji asked the masked kid if he was Katsumata, he apologisies to him and explained that he was the kid all people thought had died before a science experiment, and also says that Fukubee was actually the one who died.
Can Simeone please confirm me if this was a revision Urasawa did some time after publishing the manga originally or wtf, cos Fukubbe clearly died after Yamane shot him, so things dont add up.