文件被删案请教

I and my family have suffered a big loss by an accident so that I need
any help from you in a possible lawsuit because this case is very
special:

a few days ago, I found ALL my files in a SHARED computer were
completely deleted by someone without my permission or even notifying
me. these files included my 2-year experimental data, several paper
drafts, downloaded jounal papers, my family photos, the examples and
documents for green card application , other applied softwares,etc.
which are exetremely important to me and some of which could never be
recoveried.

the IT technology involved in this case makes me very difficult to
determine what/how to do after suffered such a big loss. so I need all
of your help to answer my following questions:

1. how could I find who did this and how he/she coud delete all of my
files without log-in my account.
2. is any department on campus in charge of such case if you think this
incident was just an immoral conduct.
3. if you think somebody's irresponsiblity has broken the law, what
should I do in the next step, to report the police station or the court
house or to find a lawyer fisrt.

thank you very much for your help, any input will be greatly
appreciated.