'Criminal Minds' finale: Erin Strauss falls victim to Mark Hamill's ReplicatorAdd to Favorites | Criminal Minds
He blamed BAU and more specifically Alex Blake. He's been taking his revenge on the team all season. In the finale, he drugged Strauss and forced her to drink, killing her. She was on to him, unbeknownst to the others, so Curtis had to take her out.
But it was her quick thinking that clued the team into his identity, as he carved a figure 8 into her wrist -- which was a planted clue in a DOJ report that wasn't actually a replication of anything. The team tracked him down to his Virginia compound, where Rossi managed to get Curtis trapped with his own explosives, taking him out.
The team buried and honored Strauss and now will turn to Season 9, which was announced earlier this month. The full team will be back.