Beginning with Android Jelly Bean, Google added support for multiple users on tablet devices. With the release of Lollipop, Google extended this support to phones. One of the most challenging problems in digital forensics has long been proving who was using a device when incriminating actions were performed, that is: Who was behind the keyboard?

Running dumpsys on the user service will show the last login info for all users:

As only one user can be logged in at a time, looking at the user with the most recent login will identify the account currently in use on the device.