bonsoir
1-
The police did not see anything when they arrived at the crime scene.(prétérit) even if earlier, the victim's neighbour had called them to report some unusual cries. (pluperfect)
2-
The policemen decided to visit he neighbour who then declared (prétérit)that he had heard gunshots from the flat next door some minutes before. (pluperfect)
3-
He wasn't relaxed at all and kept looking at the door while he was talking to the police officer. (preterit + preterit +ing)
le prétérit pour l'action passée .
le pluperfect pour une action antérieure à celle au prétérit (passé dans le passé)
preterit progressif (+ing) pour l'action dans le passé qui était en train de se faire)
bonne soirée :)