ATC...definitely screwed up, but they were calling out.
Having flown military aircraft, the H-60 specially (same helicopter), depending on the life of the aircraft and condition, radios can be really bad and hard to hear. It is reported the helicopter was on goggles. Kind of crazy to me being on goggles in a densely populated area. Lots of distractions and plumming. Let's not forget, you only have 9-11 degrees field of view with googles. An aircraft at your "90" would be hard to see. Also, what was the currency of the crew, quals, etc... Things that are rarely discussed, were any of the crew involved in personal issues, crew issues, etc. These are HUGE. I've done investigations were the crew were fighting...and lost situational awareness and crashed. It happens.
I don't have a lot of blame for the airliner. They were on final and focused on the landing, as they should have been. Not sure if they had collision avoidance gear or not. Not all military aircraft have collision avoidance due to budget, age of aircraft, etc...
I'm sticking with helicopter crew human factors on this one with a supporting factor of ATC involvement and awareness. In the end, it was people that got other people killed.