Criminal history

The task is easy, but interesting.

The purse of one of the elementary schools in the state of New York is missing. Only one of five students could steal a wallet: Lillian, Judy, David, Theo or Margaret.
When interviewing these children, each of them gave three indications:

Lillian

1. I did not take the wallet;
2. I never stole anything in my life;
3. Theo did it.

Judy

1. I did not take the wallet;
2. My dad is rich enough and I have my own wallet;
3. Margaret knows who did it.

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David

1. I did not take the wallet;
2. I was not acquainted with Margaret before I entered school;
3. Theo did it.

Theo

1. I am not guilty;
2. Margaret did it;
3. Lilian lies, claiming that I stole my wallet.

Margaret

1. I did not take the teacher's wallet;
2. This is Judy's fault;
3. David can vouch for me, because he knows me from the day he was born.

Upon further questioning, each student acknowledged that of the three statements he made, two were correct and one was wrong.
Determine which student stole the wallet of his teacher.