What kind of person is Perez?
In terms of his character, he’s not one of those haunted types with lots of problems, he’s actually a straightforward man who would just like a quiet life. Perez is a slightly idealistic guy who thinks Shetland is a safe haven - a nice, safe place to raise his daughter.
Why does he return to Shetland?
Essentially he moves back for his daughter. Cassie’s real father lives in Shetland and Perez wants her to be close to her dad because her mother has died. I think he’s got a slightly idealised view of Shetland - a place where people don’t lock their front doors.