Ethan Herd had more and more rational thoughts than Scarlett Glenn. If the person behind all this had really manipulated everything that year, then it's likely that Scarlett Glenn's every move for the past several years had been under his control.
The assassination attempt on Margaret Glenn at the Ocean City Hotel entrance might have the shadow of this person behind it, and it might even have been arranged by him.
He might have wanted to harm Scarlett Glenn a long time ago because there was also Arnold Glenn's death that year, which he likely had a hand in too.
As long as this person is not found, Scarlett Glenn's safety cannot be guaranteed, and this is what Ethan is most worried and most anxious about.
That person probably went after Scarlett that year because he felt that she was beginning to suspect something odd about her mother's death, so he wanted to silence her once and for all.
