The Columbus Dispatch creates a “photo gallery” (unattributed text) on Billy& Milligan, infamous plural system known for criminal activity in the mid-to-late 1970s and inspiration for changes to the insanity plea defense, a book, and potentially the inspiration for many movies (hint at the end of the article that unattributed author may feel that it inspired the character of Kevin& in Split as well).
Content warning: a fairly bare-bones run-down of the court cases, arrests, dates, mentions of crimes (including theft & rape), internal dynamics of Billy&, various personalities, merging therapy, a list of headmates and descriptions, many photos including Billy&’s artwork collection, institutionalization, escape attempts, and eventual death (by cancer) in 2014.
The article mentions how Ohio legislature was inspired by Billy&’s court case to change how the insanity defense works in the court of law (December 1978). Their case was grandfathered in by the old laws where the burden of proof of sanity was on the prosecution; hence Billy Milligan was found not guilty by reasons of insanity. Their plurality was clear to everyone who interviewed them and the prosecutors could not prove them “sane.” Their court case inspired legal changes to the burden of proof of “not knowing right from wrong” on the defense. A plural system can no longer be found not guilty by reasons of insanity due to simply being plural; the plural system residents who commit the crime(s) must also be proven incapable of knowing right from wrong.