It's actually really simple. Remember the mini game they had on the Heavy Rain website? All you need to do is sign up for it, and head on to this site, Precinct 52.

Upon clicking, you'll be presented to log in to the site. There's a register button below, just in case you don't have an account. Really simple stuff. Next, you'll go right straight into the evidence board. This is where you need to submit 4 different evidences, just pick, the Short Cigarette, the Origami bird, The coffee shop C (diner), and item 117h tyre tracks. Be VERY careful with the evidence, make sure you get it right. The coffee shop C for instance is pretty tricky.

Apart from that, if you got it right, head on to the evidence dossier, and you'll get your key code! Enjoy your weekend. :)