Tomorrow (Dec. 18), on the same day as the finale of the hugely popular true crime podcast 'Serial,' listeners will also be able to pick up the show's original score, composed by Mark Henry Phillips, via iTunes.

'Serial,' of course, is the weekly podcast investigating the 1999 murder of a Baltimore high school student. The breakout show has provided both water cooler conversation fodder and a timely look at the workings of the criminal justice system. It's been downloaded five million times and is currently the most-downloaded podcast in the world.

Part of the compulsive listenability of 'Serial' is derived from host Sarah Koenig's detailed investigation, as she interviews Adnan Syed -- who as a teenager was convicted of the murder -- reviews cell phone records, and chases down tell-tale pay phones.

The procedural mood is largely established by Phillips' score, a quiet, pacing thing. As former acquaintances of Syed's talk about the time he stole money from his mosque's collection basket, the score is percussive, almost funky but meditative -- accompaniment for an intrepid reporter looking for clues. A surf-y, reverb-laden guitar version of the show's ubiquitous theme moves us forward as a law clinic uncovers what might've gone wrong at Syed's trial.

"I tried to focus on Sarah Keonig's journey and what she was feeling. That was the key for me," Phillips explains in a statement. "When she finds a new piece of information she might be excited, so the music can reflect that. More than anything, like us, her biggest feeling seems to be one of ambivalence. She just doesn't know what to think. That's what I was trying to capture with the music. I wanted it to feel like you were in a foggy scene at night and you had no idea where you were."

Phillips is a former public radio reporter and producer, and he also mixes 'Serial.' In addition to the podcast, he also scores independent films and releases pop music under the name Sono Oto.

Beginning Dec. 18, you can buy Phillips' score here.

(Phillips didn't create the theme song for 'Serial,' which is actually the work of Nick Thorburn of Islands. Thorburn's theme and more music he created for the show are available to stream on his Soundcloud page.)