What crimes did he personally commit?

As the CEO he should be responsible for anything he was facilitating as part of his business, and that would include crimes committed using telegram that he was aware of and both did nothing to remove from his service and made it harder for law enforcement to prosecute. You know, like how a warehouse owner who knowingly sells space to pedos and does what he can to keep the police from searching the warehouee is complicit.

There are some circumstances where they are unaware or only take halfhearted measures, but in this case it looks like he is being investigated for actively working to enable criminals, including pedos. As the head executive, he doesn’t have to do it personally if he is directing staff to make it happen.

Edit: explaining the logic behind something isn’t the same as agreeing with that logic

I’m sorry, but it’s a private messaging app! Not even the owners are supposed to know what is going on in the chats. It’s not a moderation situation - I don’t know if he rejected a request to ban accounts, but it isn’t how things are supposed to be.