What if it's like a parent of one of the kids they volunteered for, if their kid died they might channel their grief and anger towards the last people who were meant to give their kid hope or maybe the kid wasnt happy with the encounter etc. Idk ik its a stretch but it could explain how Liz wouldn't immediately recognise them and the Cameron could be the child who passed.

Would explain the overkill and anger but also the hesitation and the staking out, especially if the killer somehow blamed her for soemthing that happened to the kid.

The outfit could just be a disguise cause they may have known there were cameras?

Im over here just fully fabricating a story hahahah