Aviation expert predicts cause of deadly Washington plane crash. A rational explanation of the air crash: 2:51 mins.

[cos dem]

7. This does seem plausible

With the important caveat that anything at this point is mostly idle speculation, it does appear to me that the CRJ was on a standard approach. I also have questions about the ADSB and TCAS, which should have absolutely been enabled when operating in this airspace. If the UH60 was perform a "covert" training operation, that should be done within a MOA (military operating area) at a minimum, not in one of the busiest airspaces in the country. Even then, I question why that would be necessary, since the training itself should not need to be covert, just "here's how you would do it, if it was required".

The tower apparently asked the UH60 if it had the CRJ in sight, but it's not clear if the 60 responded (they may have been on a military frequency). Conditions were visual, so it really should be on the UH60 pilot to see-and-avoid.