Property Fraud

My father-in-law working as a property agent. He helped someone to buy a property in Palam Delhi in which he doesn't get any money. My father-in-law warned the buyer to check the property before pay. Usually, he doesn't deal in that area so he warned the buyer to go by himself and check if the property is legal. The buyer was in hurry and paid money to the seller and my father-in-law and his friends were a witness in that case. The seller was a fraud lady and sold the property which was original held by another owner. Now the buyer filed a complaint against my father-in-law and his friends. He & the police both know where the fraud lady is living but they are not arresting and making any inquiry. Rather they are forcing my father-in-law and his friends to make a settlement outside. Any suggestions on this case will be highly appreciated. Thank you for your help in advance!