Silas' defense was simple. He told his interrogators that he'd either been asleep, or that possibly he'd experienced another "fit". Regardless, he denies their charges.
"I must have slept," said Silas. Then, after a pause, he added, "Or I must have had another visitation like that which you have all seen me under, so that the thief must have come and gone while I was not in the body, but out of the body. But, I say again, search me and my dwelling, for I have been nowhere else."