Was this in reference to a story or just the sentences as they are presented here? If it is the latter, the only components a sentence truly needs to be correct in English, is a Noun and a Verb.
"The door is locked." This is a proper sentence, Door = noun, locked = verb. Locking it in the evening is just adding more detail, but still a sentence. The same applies to the next sentence, with Diamond = noun, and kept = verb.
Does this help?
I am not sure what "V3" is. For this sentence, "is" is a preposition that binds the noun (door) to the action (locked). If you remove "is", then the sentence becomes disconnected.
"The door locked in the evening." - Here it sounds as if the door locks itself, which (unless this is a fantasy novel or a new digital system), we all know to be untrue.