If you already have the video file and need a separate subtitle file (usually in .srt format), you can search these community-driven databases:
In S01E01, Chief Inspector investigates the murder of 15-year-old Sara Damiani, whose body is found in a flooded basement. At the same time, Valeria must face her own past as her mother, Lucia, is released from prison after serving 17 years for killing Valeria's father. srt file link, or Thou Shalt Not Kill - Season 2 - Prime Video
: Search for "Non uccidere S01E01" or "Thou Shalt Not Kill S01E01". It is the most comprehensive database for multilingual subs.
: In the U.S., the series is often streamed via PBS SoCal , though subtitle language options may be more limited to English. Subtitle Download Sites