-If it is really just a lookout, then he may be an accessory. But if he participated in the conspiracy, and was expressly designated as a lookout at the time, he was still the mastermind. The specific nature depends on your partner's confession and his confession.
-If there are no other statutory mitigating, mitigating or discretionary circumstances, the accessory will be determined around 11 years, and the principal offender will be determined around 12-13 years. The specific sentencing range varies from place to place.