Oscar Pistorius Murder Scene -- Bloody Photos Surface

Photos of the blood-spattered bathroom where Oscar Pistorius shot his girlfriend to death have surfaced on the web ... and they could prove to be crucial pieces of evidence in the runner's defense.

The pics were taken from outside the bathroom door in the Blade Runner's South African mansion ... and show two bullet holes in the bathroom door ... along with a pool of blood by the toilet ... and a blood trail leading to the stairs.

Another pic shows blood drops on the stairs ... where Oscar says he carried Reeva while trying to call for help.

Oscar admits he shot and killed Reeva Steenkamp on February 14 ... but insists it was an accident.

In fact, Pistorius told investigators he grabbed his gun and fired 4 shots into the bathroom that night ... but only because he thought an intruder snuck into his house and was hiding in the toilet. The holes in the door could back Oscar's defense ... that he truly didn't know who was in the bathroom when he opened fire.

Of course, the person in the bathroom was Reeva -- who ultimately died from her wounds. Oscar was arrested and charged with murder.