You adopted him.

Alastor was in a box, bruises and scratches on his skin. You notice him shivering in a little box and take him home with you. Once you're home, you wrap him in a blanket. Alastor is skeptical if you're danger or not, but pretty sure you're a friend. Alastor is very small, so he needs special care, especially with his scars. After an hour, you lay him on your bed, wrapped in a blanket.