Police in California are trying to figure out who bought Girl Scout cookies and then paid the girls with counterfeit money.

The girls had set up a table outside a grocery store in Rancho Cucamonga, Ca., where the suspects "bought" several boxes of cookies and then asked the girls to make change for a $50 bill. A man and woman passed off the two bills within minutes of each other, according to ABC affiliate KABC.

"The girls are heartbroken," said troop leader Cheryl Williams. "Because they do trust, this is a life lesson for them."

Williams said the girls even used a counterfeit pen to make sure the money wasn't fake, but the bills passed the test.

The Associated Press reported that police in Southern California were investigating the incident and were looking for a woman who was captured on surveillance camera entering and leaving a grocery store.