why do vera and lombard each conclude that the other is not U.N. owen at the beginning of chapter 10?

Lombard tells her that he does not fancy that she is the murderer, but Vera is not as sure about Lombard. She mentions to him that he does not seem to hold a high regard for human life. He reminds her that if he were to take the lives of others, it would only be for what he could get out of it.