The/a theft

Hi teachers,

Do we have to use indefinite or definite article as in 1?

She had committed the/a theft?

Would you please explain the following sentence?

Arthur’s eyes shifted as he brushed his teeth. Does it mean "Arthur’s eyes changed their position while he was brushing his teeth?

Many thanks.

The definite or indefinite article are both grammatically acceptable in that sentence. The one you require would depend on the wider context.
a theft - unspecified
the theft - the one being discussed.

It means he looked from one place to a different place as he was brushing his teeth. (His gaze moved, not the eyes themselves).

Thank you very much. Do we have to translate the second part in past continuous?

She had committed murder.
She had committed a murder.
She had committed suicide.
She had committed a suicide.
She had committed crime.
She had committed a crime.
Please correct the above sentences.

‘She had committed a suicide’ is highly irregular because there is only one possible suicide she could commit. Because of the nature of the act, the structure does not follow the same rules as the other sentences. We don’t speak about committing ‘a suicide’ or ‘the suicide’.

As for the others:
The sentences without the article are less specific than the ones with the article because they give no indication of how many murders/crimes had been committed.
The sentences with the indefinite article indicate that she had committed one murder/crime.
If you used the definite article, the indication would be that the murder/crime committed was the one under discussion in the wider context.