Mr Sane

Well, I got an idea, I thought of Au where BB lived and years later after L's death and Near's upcoming as the new L, BB escaped and learned fairly quickly L has died and there was a new "L"

He decided to create crimes and much to his last murders and puzzles, He placed the initials 'L' and 'N' which caught the attention of Near who took this as a challenge to find the killer.

They later worked together to figure out the case, both being extremely suspicious of one another as the killer and the detective.

Near: "keep your friends close, and the suspension on someone being the killer, Closer.."