From the beginning, there were issues involving evidence collection. An important bloody fingerprint located on the gateway at Nicole Simpson's house was not collected, secured, and entered into the chain of custody when it was first located. Although it was documented by Fuhrman, one of the first detectives on the scene, in his notes, no further action was taken to secure it.
The detectives who took over Fuhrman's shift apparently were never aware of the print; eventually the print was lost or destroyed without ever being collected. Other items of evidence were also never logged or entered into the chain of custody, which gave the impression that sloppy forensic collection had been carried out at the scene.
The prosecution had expert witnesses that testified that the evidence was often mishandled. Photos were taken of critical evidence without scales in them to aid in measurement taking; items were photographed without being labeled and logged, making it difficult, if not impossible, to link the photos to any specific area of the scene. Separate pieces of evidence were bagged together instead of separately causing cross-contamination; and wet items were packaged before allowing them to dry causing changes critical evidence.
Nicole Brown's body was covered with a blanket which came from inside the house, this completely contaminated the body and anything the blanket touched around the body. Beyond poor evidence collection techniques, sloppy maneuvering at the scene left more bloody LAPD shoe prints at the scene than perpetrator prints, again giving the appearance of forensic ineptitude.
Securing the Evidence
Throughout the investigation there were issues with how evidence was secured. There was about 1.5 mL of O.J. Simpson's blood assumed to be missing from a vial of evidence. The reason this idea of "lost blood" could not be countered by the LAPD was because there was no documentation of how much reference blood was taken from Simpson as evidence. The person who drew the blood could only guess he had taken 8 mL; only 6 mL could be accounted for by the LAPD.
To add to the problem, the blood was not immediately turned over as evidence but was carried around for a few hours before it was entered into the chain of custody, allowing for speculation of when and how the 1.5 mL of blood may have disappeared.
The security of LAPD storage and labs was also brought under scrutiny when it was found that evidence was altered or was given access to by unauthorized personnel. Simpson's Bronco was entered at least twice by unauthorized personnel while in the impound yard; Nicole Simpson's mother's glasses had a lens go missing while it was in the LAPD facility.
A Question of Planted Evidence
Not only were there many claims that the evidence was mishandled in the police lab but there were also claims that evidence was planted at the crime scene. Because the police department did not have proper collection documents regarding Simpson's blood, it was said that the police planted Simpson's missing blood on critical evidence and in critical areas of the murder scene.
The defense team stated that EDTA was found in the samples of blood that were collected at the crime scene. EDTA is a blood fixer (anticoagulant) used in labs and mixed with collected blood; if evidence with Simpson's blood showed traces of EDTA, the defense claimed, then that blood had to have come from the lab, which meant that it was planted.
However, EDTA is also a chemical found naturally in human blood and chemicals such as paint. At the time, tests were not readily available to differentiate between natural and contaminant EDTA or the differences in the levels of EDTA in blood between EDTA from a tube and naturally occurring EDTA. Some believe that the positive EDTA results may have been due to contamination of the equipment used to run the tests.
A Question of Character
Mark Fuhrman, one of the first detectives on the scene, was discredited by the prosecution when he was alleged a racist and was accused of planting evidence. He perjured himself on the stand and when asked if he had falsified police reports or planted evidence in the Simpson case he invoked the 5th amendment, the right against self incrimination. This put anything he touched in the investigation under scrutiny.
Fuhrman was accused of planting critical evidence, contaminating it with Simpson's blood, and of falsifying police records. In Fuhrman's book he stated that at one point he was even accused of killing Nicole Brown and Robert Goldman himself.
Understanding Forensic Science
A major hurdle that the prosecution team failed to overcome was the lack of knowledge and understanding regarding forensic science, specifically DNA. The jurors agreed that the DNA testimony was difficult to appreciate since expert witnesses were not able to put their evidence in terms that the jury could understand.
This inability to understand key evidence made the evidence essentially useless, even some seasoned lawyers found the scientific testimonies to be incomprehensible. It is reported that the DNA evidence showed that the chance that some of the blood found near the bodies came from anyone but Simpson was one in 170 million. The chance that blood found on Simpson's sock could be from someone other than Nicole Brown was one in 21 billion.