Arrest him

"What happened? Do you know what killed him?" Mar nearly tackled the poor Ima to the floor, with his questions.

He was impatient to know what killed his father. 

"He was killed with poison from the river," the Ima said immediately after the prince asked him. He glanced around the room, "the king was killed with the poison he injected. The poison was given to him directly, that was why it affected him drastically." The Ima said with an expressionless expression on his face.

"How did he get poisoned? His room is well guarded. No one else would have done this if not for someone he knew. Someone who will freely walk into the king's Chambers without arousing suspicions from those around."

"You were the last one here!" The queen suddenly shouted as she pointed to Osy whose eyes were widened.

"What?" Both Cyp and Osy exclaimed, while Mar levelled the queen with a gaze as fiery as his anger.