People know when they're being tested, so be upfront about the tests. Give clear clean scenarios from your time with the company, asking them what kinds of calls they would have made as a manager.
Don't look for the "right" call, but do look for calls that seem to suffer from "skin deep" analysis. For example:
An employee who's had problems on two teams is having problems after being
moved to a third team. His team mates just called for a corrective
action due to his complaints in a review of the current work. The
team is upset, and says they're not happy with his work. What would
If he starts describing how to eject the employee out of the company, by preparing the paperwork proving the employee's inability to work with a team, he's going to be easily manipulated. He doesn't have enough information.
If he starts describing how he would gather information to make a call on if the team's description is accurate, he's about as good as you can get.
Decisive action in a manager is game-able by the problem elements in every organization. Typically the manager figures out they're being played a year or so down the line, but by then the culture has taken a major hit.
As far as the rest of it goes, try to get some insight to his grades (even if they are way back when) at University and where he went to school. While experience is vital for success, this person probably has experience, and it is probably dressed up in its best presentation. Grades can't be doctored in such a manner, and can be a better predictor of success than your ability to discern if this person is a good fit.