Something disturbed and shocked him.

At the bottom of his heart, he felt ill at ease.

He had triumphed; but his victory gave him only uneasiness, pain, and vexation.
A reflection so simple that he could hardly understand why it had not occurred to him at first, increased his discontent, and made him angry with himself.
"Something told me," he muttered, "that I was wrong to undertake this business.

I am punished for not having obeyed that inner voice.

I ought to have declined to proceed with the investigation.