Animation: Up Action vs Back


I noticed that when I am in the child activity with the crime detail and press

  • the Back button, the child activity “fades out” and the parent activity with list of crimes is shown
  • the Up navigation button, the parent activity “fades in”, same animation like if I am starting a new activity

I tried how it looks like in the Contacts app and there it is consistent, both back and Up causes the child activity to fades out.

How this can be done?