Habeas, retroactivity (Posner)
Although Federal Habeas is unavailable for 8A claim as it was not raised on state direct appeal, there is sufficient cause & prejudice for a successive state Habeas. A post-sentencing Supreme Court holding establishing a categorical bar to mandatory life sentences for juveniles also established a non-categorical right for juvenile status to be considered in mitigation when imposing a life sentence.
Dissent: The ethic behind the non-categorical right was present in earlier decisions as well. Problematic rule.
http://media.ca7.uscourts.gov/cgi-bin/rssExec.pl?Submit=Display&Path=Y2016/D01-04/C:14-1944:J:Ripple:dis:T:fnOp:N:1681279:S:0
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.