When a policeman is killed in the line of duty their call sign or car number is retired permanently. Basically that's what was happening in this audio clip. Its a tribute to the sacrifice the officer made...

The dispatcher tries to raise the officer over the air, the officer doesn't respond...its done 3 times then a supervisor asks for a time check. If you notice the time check will say NOV 1, 940 am....even though it was NOV 14... that was done because that's what time the supervisor would have expected 35S3 to answer....then the supervisor says take 35S3 off the air for good...job well done... (less info)