Chief Justice John Roberts flipped late in the game on the Supreme Court ruling on "Obamacare" and ended up writing both the majority opinion and most of the opposing dissent, sources said Tuesday.
Supreme Court experts described the move by Roberts, whose decisive swing vote to uphold President Barack Obama's overhaul of the failing US health care system, as unprecedented.
The ruling on the reforms, Obama's signature domestic policy which aims to provide insurance to most of the 50 million Americans who lack it, was written in such a way that one can tell it was at first rejected, they say.
Internal sources -- both independent and within the court's jurisdiction -- confirmed Roberts changed his stance on the law during the three months of deliberations, prior to delivering the stunning decision on Thursday.
"Roberts did change his vote fairly late in the process," professor of law at the University of Colorado at Boulder, Paul Campos, told AFP, based on his sources, which confirmed an earlier report from US broadcaster CBS.
Joining the ranks of four progressive judges, Roberts, who was appointed by Republican President George W. Bush, saved Obama's legislative opus from being struck down by the majority conservative court.
As is not unusual, Roberts chose to write and deliver the ruling of the 5-4 majority, reading it aloud on Thursday.
But Roberts also wrote "three quarters" of the dissent, where the minority explains its reasons for opposing the decision, Campos wrote on news site Salon, citing a source "within the court with direct knowledge of the drafting process."
"What is very unusual is for someone to end up in a position where they end up offering large parts of both the majority and the dissent. That's unprecedented," Campos told AFP.