It's been a while since I flew in/out of DCA, but I would swear I always landed from the north on Runway 22. I might be mistaken.
DCA prefers to use runway 01 for departures and arrivals. Putting smaller aircraft on 33 allows for higher landing rate with departures on 01.
01 arrivals are either the Mount Vernon visual or ILS, and then a circle to land on 33 from those arrivals. 01 departures follow the river to avoid overflight of the Pentagon, White House, and monuments.
Landing on 19 requires the river visual, which winds around over the Potomac, avoiding those same areas, and while 15 is available for landing, it is still short, and taxi back from the end of that runway requires crossing others, and I don’t think 22 has been used for a while because you have to be quite a slow airplane to make the turn and stay out of the restricted areas, so, landing south reduces the arrival rate.
DOD aircraft are exempt from the key parts of operating in the DC FRZ and don’t need a flight plan or squawk (transponder code). I suspect that was the case with this H-60, which would mean that TCAS on the CRJ would not have seen them. H-60s don’t have TCAS and both conflict aircraft need to have TCAS installed for the system to work.
The H-60 and CRJ were up the same freq. The H-60 was told to report the CRJ in sight and to pass behind the CRJ.
But to an Army helo driver not used to high density operations, "report the CRJ in sight" and "pass behind the CRJ" may not have been clear. They see one jet and think they have the "CRJ" in sight, not knowing it's circling for 33, when, in fact, they're looking at a different airplane lined up on 01. "CRJ" may not have any meaning for them - it's just another airliner.
Having worked extensively with the US Army while at the CAOC in Al-Udeid, the Army views aviation differently than everyone else. They own* all airspace below 500 feet and have no need* to worry about other traffic. No need* to coordinate. No need to de-conflict in “their” space.
*Completely false, of course, as Joint Pubs and regulations require that coordination and the Army does not own that space, but that is the prevailing attitude. It is pervasive.
That same attitude led to the 1994 shoot down of an H-60 by an F-15 when it was operating in Iraq - The H60 had no flight plan, no squawk, no need to coordinate with other agencies.
I imagine that the DOD exemption for operating in the DC FRZ will be amended.