Swamped

You think you can risk a confrontation, as long as you're not too direct. You tap the thief on the shoulder.

"You seem awfully protective of your pouch. Are you hiding something in there? Such as a talking lizard?"

They're clearly extremely nervous, but the last bit of the question seems to have them confused.

"A lizard? Why would I... I mean... What are you talking about?"

Their nervousness seems strange, actually. Good enough to grab something from your pocket unnoticed, and yet clearly unprepared for a confrontation? Why would that be...

Because they realize what they stole. It was more than they bargained for. They're not involved in all the criminal infighting, and probably don't want to be.

That's all just a hunch. But if it's true, then you might be able to use it to your advantage. You just need to think about how.