Have the burglar lie to them, which sends them into a trap. At he trap is some person or clue to who is really responsible.
And, by the way, just because he's got high motivation to keep his mouth shut, does not mean he has the willpower to do so under duress. Unless he's got an indomitable will (high wisdom, on a burglar?), he may squeal.
Also remember that the PCs are many, and you are one - so the players can always out-think the GM, given time and information. Just because you have not thought of something that will get him to talk, does not mean that they won't.
And, by the way, just because he's got high motivation to keep his mouth shut, does not mean he has the willpower to do so under duress. Unless he's got an indomitable will (high wisdom, on a burglar?), he may squeal.
Also remember that the PCs are many, and you are one - so the players can always out-think the GM, given time and information. Just because you have not thought of something that will get him to talk, does not mean that they won't.