Quiz

I want to present my solution to the riddle of who stole the teacher's wallet once again. Yes, Yashchur solved it correctly before me; I just want to write down my correct solution, as I intended to do that time, since the previous one was incorrect.

Let the statements that they didn't do it be:
Lilian - a,
Judy - b,
David - c,
Theo - d,
Margaret - e.

Lilian states that she has never stolen anything in her life - f
Judy's father is rich - g,
Margaret knows who stole it - h,
David is not acquainted with Margaret - k,

Then:
Lilian: a+f+(1-d)=2, a>=f
Judy: b+g+h=2
David: c+k+(1-d)=2
Theo: d+(1-e)+d=2
Margaret: e+(1-b)+(1-k)=2
a+b+c+d+e=4

Then, from the fourth equation, we get that d=1 and e=1
From the third equation, we get that c=1 and k=1
And from the fifth equation, we get that b=0

The trick is that Lilian's statement should be written as a+f+(1-d)=2, a>=f, because the situation where a=1, f=1 is possible, a=1, f=0 is possible, a=0, f=0 is possible, if we don't take into account that two of her statements must be true, but a=0, f=1 is not possible... that is, we need to add a>=f