About the siren thing...it could have been that whoever called asked for a silent approach. We've done it multiple times for my dad's heart attacks or my grandmother's broken hip. Having them arrive in the middle of the night in full blast wouldn't be appreciated by the neighbors and it only adds to the stress really.
Or it could have also been that the "tragic death" had already occurred when the call was made, and while you need investigators, you don't need them in lights-and-sirens mode.