To use the old bullshit that everyone trots out whenever secrecy or privacy is mentioned.
It may be that there is nothing there but we won't know unless it is investigated properly.
You could claim that this, like the tax release and Trump's overall buffoonery, are diversionary tactics to dilute opposition to policies like tax cuts for the rich, healthcare, environmental cuts but he does not seem that devious. Or he is that smart and excellent at playing an arrogant and naive liar.
I don't think that theory has merit either. But in the hypothetical situation, the diversion would be pushed by the business interests who are benefitting from Trump slashing environment protections, regulations, and corporate taxes. The same business interests that contribute to both left and right arms of the Business Interests party.
Edit: I didn't see your opening line about investigators.
It is noble to remain neutral and wait for evidence. It is good to take anonymous sources with a grain of salt. But everyday people make character judgements based on circumstance, like avoiding the scammers playing 3 card monte, or seeing the mountain of circumstances around Cosby and O'Reilly.