Oscar Pistorius trial: The pieces of the puzzle

Johannesburg: A toilet door, a gun, an iPhone - and some prosthetic legs. A stray bullet and the difference between a man and a woman screaming. All are pieces of the Oscar Pistorius puzzle that will likely be scrutinized at the Olympian's murder trial starting Monday.

A glance at some of the possible evidence:

THE TOILET DOOR

Pivotal from the outset, the bullet-marked toilet door through which Pistorius shot was removed from his home in the hours after he killed Steenkamp and was held by police. It was taken back to the house last year to be re-hung while forensic experts working for Pistorius' defense recreated the scene. Both sides know its value.

If grouped together, the bullet holes could suggest Pistorius at no point fired a warning shot and therefore may not have been thinking about self-defense but rather had a direct intention to kill. Even if he can show he didn't know it was Steenkamp behind the door, Pistorius could still be found guilty of murder, legal experts say, because he shot with intention to kill someone.

And what about the stray bullet? Investigators initially missed one bullet that did not hit Steenkamp and which was later found in the toilet bowl. Pistorius fired four times and she was hit three times, in the head, arm and hip. Could this bullet be the warning shot to show Pistorius was trying to warn an intruder? A hole in the door may tell.

PROSTHETIC LEGS

The height of Pistorius' prosthetic legs will show how tall he stands when he is using them and how much lower he is when on his stumps. If that is matched with the height of the holes in the door and eventual trajectory of the shots into the toilet cubicle it should conclude whether Pistorius was or was not wearing his prosthetics. It's important because the two sides disagree. Pistorius says he was only on his stumps. Prosecutors say he took the time to put on his prosthetic legs before killing Steenkamp, and therefore had time to plan a murder. Proof either way will help one side and harm the other.

THE IPHONE AND A 'SMOKING GUN'

Investigators have been chasing information on Pistorius' locked iPhone for months and may have finally accessed it in the days ahead of his trial through a meeting with Apple officials in the U.S. Is Pistorius' claim that he forgot the password to his phone suspicious and an attempt to hide something? And what about the records on Steenkamp's phone, also found among a number of cellphones in the bathroom?

Communication with third parties on cellphones hinting that Pistorius' was angry or that Steenkamp was fearful could be the 'smoking gun' that shows that all was not well between the couple.

PISTORIUS' GUN

Little has been revealed about where and in what condition Pistorius' 9 mm Parabellum pistol was found after the killing but prosecutors think those details help their case and show it was murder.

SCREAMING

Pistorius says he screamed for the perceived intruder to get out of his house before shooting, but Steenkamp was silent throughout. Prosecutors say a woman was heard screaming before the fatal shots. If it can be shown that a woman was screaming, then the suggestion is that Pistorius must have known where Steenkamp was and can't have shot her by mistake, and that they were fighting. But if the defense can cast doubt on claims of screaming and an argument, as Pistorius lawyer Barry Roux did at the bail hearing, the prosecution loses a significant part of its case.