The original with "been being watched" feels like something the detective says when he first discovers the fact about watching. It has an exclamative aspect to it. There's a present sense of realization, mixed with the past sense of when the watching had taken place.
"She would have had to have been observed." is something like a lawyers distillation of what happened later for the court.
The original with "been being watched" feels like something the detective says when he first discovers the fact about watching. It has an exclamative aspect to it. There's a present sense of realization, mixed with the past sense of when the watching had taken place.
"She would have had to have been observed." is something like a lawyers distillation of what happened later for the court.