Another idea

I thought a different approach to Ollie's plot idea would work well. Instead of using a sound effect such as a police siren, implement some non-diagetic music, I was thinking something classical, yet tension building. Either that or the killer can have visible earphones in, and therefore make the song seem diagetic, whichever will have more effect and incorporate into the rest of the video better. I thought the song, The taste of regret, by In Fear And Faith would be effective for this as the piano, drum and violin mix intro that lasts about 22 seconds would work really well. The drums slowly builds in tempo and volume, and helps to ease the audience into the flow, so that the drums rise with the tension. Also to make the music work well in contrast to the footage, the camera should be following the anonymous killer as he/she walks whilst the intro plays. considering the length of the intro this would probably have to be a part of our footage, as it would only be about 20 seconds long. I have linked the song below, listen to the first piano intro, and the music will cut out just before the guitar kicks in.