Credibility, or so it would probably seem to him. Any real investigator would never out himself like that, especially on day 2. And I'm more likely to believe Serah than the crazy guy roleclaiming on day 2.
However, I've seen this plenty of times in newbie players playing mafia goons and the lack of experience, plus lack of direction causes them to do something this stupid. The only redeeming thing about it is that usually even the newbies aren't THAT stupid. But I'll keep my vote on him until I see something more scummy.
And congratulations, you're on my list now. I'll keep an eye (and spear) on you.