Homework help please...thanks in advance:-)?

You have just arrested two suspected gang members for painting graffiti—gang symbols—on the courthouse wall. They are in custody and have invoked their Miranda right to silence. You decide to place them in the same police car with a hidden tape recorder running to see if they make any incriminating statements. The tape recording, made while you were outside the car, reveals that the gang members discussed committing the crime and concocted an alibi to give to the police. Have you interrogated the suspects or violated their right?