The first of the keys, the Lion key, is found in the trunk of a police car. The car has stopped to a holt at the edge of a caved-in road (which slants downward to the river), leaving behind a trail of tire skid marks. The car's windshield however, is broken in front of the driver's seat and has blood streaking away from it. Reader's of Oz may be familiar with this scene:
The Wonderful Wizard of Oz wrote:_____This was to be an eventful day for the travelers. They had hardly been walking an hour when they saw before them a great ditch that crossed the road and divided the forest as far as they could see on either side. It was a very wide ditch, and when they crept up to the edge and looked into it they could see it was also very deep, and there were many big, jagged rocks at the bottom. The sides were so steep that none of them could climb down, and for a moment it seemed that their journey must end.
_____"What shall we do?" asked Dorothy despairingly.
_____"I haven't the faintest idea," said the Tin Woodman; and the Lion shook his shaggy mane and looked thoughtful.
_____But the Scarecrow said: "We cannot fly, that is certain; neither can we climb down into this great ditch. Therefore, if we cannot jump over it, we must stop where we are."
_____"I think I could jump over it" said the Cowardly Lion, after measuring the distance carefully in his mind.
_____The Scarecrow sat upon the Lion's back, and the big beast walked to the edge of the gulf and crouched down.
_____"Why don't you run and jump?" asked the Scarecrow.
_____"Because that isn't the way we Lions do these things," he replied. Then giving a great spring, he shot through the air and landed safely on the other side. They were all greatly pleased to see how easily he did it, and after the Scarecrow had got down from his back the Lion sprang across the ditch again.
Assuming this, one could say the driver crashed into the edge of the ditch (after skidding) and "sprang" out of the windshield onto the other side. Or the car skidded to a stop after something jumped through the windshield. The idea of the cop car can also resemble the idea of "standing-up" to authority (Courage + Cop).
Next is the Woodman key, accessed through an "Off Limits" gateway behind Cafe 5-to-2. We see a basketball hoop splattered in blood with a dog's head beneath it on the ground: a trail of blood extends to the key. This part is obvious for Oz readers:
The Wonderful Wizard of Oz wrote:_____So the Woodman raised his axe, and as the wildcat ran by he gave it a quick blow that cut the beast's head clean off from its body, and it rolled over at his feet in two pieces.
This, of course, isn't the only time the Tin Woodman beheads another. He kills 40 wolves this way later in the story, leaving behind a monstrous pile of bodies. The reason the dog was killed must resemble the Woodman's motive of protecting innocents. But the question of the key is: where did the dog's body go? And why was it's head used as a basketball?
The final key, the Scarecrow key, lies dormant in a bloody mailbox. The only way to access it is to cross a set of wooden planks, over a rocky ditch. This applies to the second ditch the party encounters in Oz:
The Wonderful Wizard of Oz wrote:_____The Lion was about to reply when suddenly they came to another gulf across the road; but this one was so broad and deep that the Lion knew at once he could not leap across it.
_____So they sat down to consider what they should do, and after serious thought the Scarecrow said:
_____"Here is a great tree, standing close to the ditch. If the Tin Woodman can chop it down, so that it will fall to the other side, we can walk across it easily."
Scarecrow Key Description wrote:"The key to the garden of the house. Found in mailbox blocked by a fallen tree."
The ditch has the same meaning in both the game and book: continuing the journey, the hope. But the mailbox puzzles me. It's shaped almost like a house or barn and has blood "pouring" out of it. Maybe representing the Scarecrow's creation or Dorothy's grey Kansas?
Other things to note are the health drinks found with the Scarecrow and Woodman keys (used to sustain life) and the handgun ammo found with the Lion key (used to take life). Also, the locks on the door are in the opposite order of the character's introductions in the book.
P.S. I took the pictures using my digital camera on my TV, so I know they look choppy. But they illustrate my point nonetheless.