A little search would have easily given you the results, but nevermind. I am in a good mood. :)

First and foremost the easiest is to have an array of audio files and play them one of them randomly when you press the J key.

var swatCommands : AudioClip[]; // Add your audio files here in the inspector.

function Update (){
if(Input.GetKeyDown("j")){
    audio.PlayOneShot(swatCommands[Random.Range(0,swatCommands.length)]); // Choose a random clip here.
    }
}

@script RequireComponent(AudioSource) // Make sure the object has a AudioSource attached.

It should work. I may have spelled length wrong, but the compiler should tell you if I did.

That is properly more or less the basics of randomly choosing a file from an array.

Good luck!