Had committed is the past perfect.
The past perfect tense is had committed.
The past perfect tense of "commit" in the sentence would be "had committed" – the detectives believed that the maid had committed the theft.
Existed is the past tense. The past perfect tense is had existed.
The past tense is bled, and the past perfect tense is had bled.
The past tense of sit is sat; the past perfect tense is had sat.
The past perfect tense of hope is had hoped.
The past perfect tense is had submitted.
The past perfect tense is had chosen.
The past perfect tense is "had confronted".
The past perfect tense is had set.
The past perfect tense is had burned.
The past perfect tense is had rung.