This puzzle is not mine, but I couldn't find an original source. I edited it somewhat.
An elementary school teacher had her purse stolen. The thief had to be Sammy, Karin, Arnold, Harry, or Liza. When questioned, each child made three statements:
(1) I didn’t take the purse.
(2) I have never in my life stolen anything.
(3) Harry did it.
(4) I didn’t take the purse.
(5) My daddy is rich enough, and I have a purse of my own.
(6) Liza knows who did it.
(7) I didn’t take the purse.
(8) I didn’t know Liza before I enrolled in this school.
(9) Harry did it.
(10) I am not guilty.
(11) Liza did it.
(12) Sammy is lying when she says I stole the purse.
(13) I didn’t take the teacher’s purse.
(14) Karin is guilty.
(15) Arnold can vouch for me because he has known me since I was born.
Later, each child admitted that two of his statements were true and one was false. Assuming this is true, who stole the purse?