Police have arrested a woman for passing fake money at local stores, and they think she could just be the tip of the iceberg.

Officers came across 18-year-old Cassandra Castro while investigating a completely different crime.

They said she and another woman were caught stealing clothes from Macy's at River Center mall by stuffing them into their empty purses.

"When they arrested her for shoplifting, it's protocol for the officers to run a warrant check on everyone they arrest. This officer ran a check on this suspect and found that she had an outstanding felony warrant," SAPD officer Matt Porter said.

Police said Castro also used two fake hundred dollar bills at two different Target stores.

Video surveillance from the Target in the 700 block of NW Loop 410 shows a woman making a purchase with a hundred dollar bill back in January.

Investigators say video from Target in the 5300 block of West Loop 1604 shows the same woman buying gift cards with fake funds, and they believe it's Castro in both videos.

A loss prevention investigator for Target brought the money to secret service agents and they confirmed that the bills are fake.

They also think there could be more bills out there.

"Secret service actually went out and investigated all the evidence that was collected at this particular target. They do believe this individual may be part of something bigger," Porter said.

Now they're hoping to move up the ladder to arrest the masterminds behind it.