The next day: Le lendemain
The police arrived: la police est arrivée
At the shop: au magasin
To determine: pour/afin de déterminer
What the thief had taken: ce que le voleur avait pris
notes: Allow la gendarmerie for la police although it refers more to the police force. Must have agreement on arrivée. Do not allow le jour prochain for le lendemain -inauthentic.