[Alberta's Child]

There's one monkey wrench in your scenario:

If Roberts leaked the draft in an attempt to sway one or more of the other five justices, it would be highly likely that their reaction would be the exact opposite of what he intended.

1. The justices would lose confidence in each other, and in HIM.

2. They would likely be very pissed off at him.

3. They would see the failure to identify the "leaker" as an indictment of him as the Chief Justice.

[Stravinsky]

Then your view is someone from the conservative side leaked it.