Leads are followed until they reach a dead end...What I see are nothing more than excuses from the WH.
Why did Lt Col Vindman's brother get booted from the WH? He had nothing to do with trump's Quid Pro Quo, or his twin brother going to the NSC's lawyer, expressing his concerns about the conversation of the phone call he listened to between trump and Pres Zelensky.
BTW --- not having first-hand knowledge won't prevent you from giving testimony. This is what the majority of investigations, LAW ENFORCEMENT, starts with.