You didn't need to find Miriam, she found you. When the guards saw the man you brought in, they called the captain over, who was still being pestered by Mariam. But when she saw the thief she didn't hesitate to go over to him and take the shield off his arm and the spear from you. "Where's my holy symbol? It's a golden holy symbol to the Dawn Star!" 

Meanwhile the captain came over and looked at the thief. "Garruk. I should've known." The man snorted and spat at the captain's feet. "This wouldn't have happened if you just let me on the force, Yhorn! I'm tougher and stronger than all of your men!" The captain, Yhorn, shook his head. "Strength doesn't matter when you can't even follow orders Garruk. You're no better than bandits if all you do is use that strength of yours to rob others." The captain looked at you and nodded. "Thank you for your assistance. I honestly didn't expect to see this man again. We'll take him into our custody. Oh, and we'll let the kobold go free too. I honestly didn't think he was the thief, but everyone pointed their fingers at him."