The evidence that is available in the packet and any other information they deem relevant to the case.
Each decision authority might handle separation review differently. One might read through the entire packet, another might skim the packet and rely on staff principles to do most of the reading and back brief the decision authority.
In some cases the decision authority might speak with the chain of command (battalion and company commanders). In cases involving the suspension of the separation action the decision authority might speak with the NCO support channel.
The Soldier could also take their concern straight to the commander making the separation decision. The Soldier can explain the situation from their perspective. The Soldier should be organized and have a well prepared written statement (that was reviewed by JAG). Using this method gives the decision authority first hand knowledge of the Soldier and their side of the story. Soldiers using this step should request to see the decision authority on open door policy to discuss the matter. They can also request that the separation action be placed in suspension similar to an Article 15 punishment suspension.