How to hack into a deceased person's Mac that is still running? This is kind of an unusual question: a (non-technical) friend of mine (quite literally) on the other side of the world finds herself in the following situation: 

A person died unexpectedly, their Mac is still running and displaying the Lock Screen, and nobody has the password nor any sort of technical expertise. They would like to get access to at least the data on the disk, maybe also the account. They are currently afraid to shut down the computer because it displays a warning about unsaved files.

Is there any chance they can get into the account from the Lock Screen? I guess not.

Failing that, what would be the easiest way to gain access to the data (after a forced reboot)? Single User Mode?
If your friend have something like family documents which can prove the relationship between him and his passed one, then try to contact Apple for solution. They do solve sort of situations like this :)