Past Perfect Progressive

(a) The police had been looking for the criminal for two years before they caught him.
(b) Eric finally came as six o'clock. I had been waiting for him since four-thirty.
The past perfect progressive emphasizes the duration of activity that was in progress before another activity or time in the past.

(c) When Judy got home, her hair was still wet because she had been swimming.
(d) I went to Jane's house after the funeral. Her eyes were red because she had been crying.
This tense also may express an activity in progress close in time to another activity or time in the past.