警察正在调查他的犯罪动机。

jǐngchá zhèngzài diàochá tā de fànzuì dòngjī.

The police are investigating his motive for the crime.

在了解嫌疑人的动机后，调查取得了重要进展。

zài liǎojiě xiányírén de dòngjī hòu, diàochá qǔdé le zhòngyào jìnzhǎn.

After understanding the suspect's motive, the investigation made significant progress.

我不太明白他这样做的动机。

Wǒ bù tài míngbai tā zhèyàng zuò de dòngjī.

I don’t really understand his motive for doing this.