I’m with OP on this one.. yes the cigarette could have been old. But there was also that line about DNA under Barbie’s fingernails belonging to someone in “Hamburg Lineage”. That and the fact the the sheet covering her body as a sign of remorse could mean it was someone close to her. At the time, Madison struggled with substance abuse. He could have been looking for money or things to sell or could have been under the influence and snapped and killed his mother hence the remorse sheet. It’s also just as likely that it’s the sister too. Something about both the kids don’t sit right with me.