When Vijay and IGP were watching the footage from the CCTV to prevent David from killing Dr. Varma, there was no audio from any of them. However, there was an audio from the two constables boasting that David will kill Dr. Varma even if Vijay and IGP made special arrangements made to prevent it from happening and that they will lose their jobs. So it's unrealistic how that audio was heard while the other screens did not have any audio at all.