Any stories where the hero properly explains why he knows the bad guy's bad?

[BWTraveller]

I know it's an odd request, but I've seen this several times and it gets old. The hero sees direct proof that someone is a scheming villain, but while he tries to convince others of this guy's villainy, he doesn't just come out and say exactly what happened. Eventually things have to come to a head before people finally believe him. I always find myself thinking "why didn't he just say that he saw this or this guy said that".

Two examples of the scenes I'm talking about:

Spoiler for Nurse Angel Ririka:

Kanon is killed partway through the series, then comes back secretly brainwashed by the big bad Dark Joker. Seiya gets more and more suspicious of him and Kanon constantly tries to use that suspicion to encourage Ririka to doubt and reject him. Eventually he directly reveals his true colors, trying to lock Seiya up while he seeks Ririka's life. Seiya afterward proceeds to try various things, but the one thing he doesn't do is tell her that the guy locked him in a room and talked about how hard he'd worked to separate them. He almost never says exactly what he'd experienced until he forces a confrontation and gets nearly killed forcing him to expose himself.

Spoiler for Salad Days:

In an old romantic manga called Salad Days, in the piece "Strange Couple", the male lead gets worried when a guy who is known for seducing women and dumping them after one night, even beating them if they won't accept that he's done with them, goes after his childhood friend. She walks with him, depressed because the ML recently got a girlfriend, and buys into his claims that the rumors are exaggerated and troubling; the ML follows them out of concern and sees the guy kiss her. The next day he's alone on the rooftop when the bastard shows up and starts to brag about how easy girls like her are, how fun it was to deliberately kiss her in front of the ML to further his seduction, and recommends that he use the same techniques after he dumps her. The ML furiously punches him only for his childhood friend to show up and furiously tell him off for attacking someone over nothing but malicious rumors. He proceeds to desperately interfere and ensure that the two won't be alone so at the least the guy won't be able to complete his goal, which only angers her more. The one thing he doesn't do is try to get her alone for just a minute to tell her that no, he didn't punch the guy over a rumor; he punched him for calling her easy.

I understand why this's done. Especially in cases like above where you're dealing with a guy who cares about a girl who likes or is involved with the bad guy. It's far more dramatic to have the bad guy reach a point where he directly shows his true colors and nearly does something irreversible. Even so, just once I'd love to see a story, be it manga, LN or anime, where the hero spells out plain as day exactly what happened, what the person did that led to his conclusion that this guy is an enemy.