Scammers call a victim and claim to be a local officer or federal agent and tell the person they have an active warrant. The scammer then says the person must send money using a credit card, gift card or prepaid debit card to clear up the warrants.
Police will never call you on the phone to demand money to clear up active warrants.
Also, check with local police to make sure that any officer who calls soliciting charitable donations is actually an officer, or with local officers to make sure that a company claiming to represent the police department is truly collecting for charity.