On the night of June 12, 1994, Nicole Brown Simpson and friend Ron Goldman, were killed between the time of 10 P.M. and 12 A.M. They were killed with a knife at 875 South Bundy Drive (Nicole's townhouse) in Brentwood, California. Orenthal James (O.J.) Simpson, ex-husband of Nicole Brown Simpson, was charged with two counts of first-degree murder.
A large quantity blood was found at the Bundy estate and at the Rockingham estate. A trail of blood was found at the actual crime scene as well as in Simpson's white Bronco and at his house. The walk and the rear gate at the Bundy estate had blood from Simpson. This was determined by using genetic fingerprinting. The blood of Nicole Brown Simpson matched the bloodstains that were collected at the crime scene (Nicole's house) and at O.J.'s house.

     Blood with DNA that matched Simpson's was found at Brown's condo. Blood spots in Simpson's car contained DNA matching Brown's, Goldman's and Simpson's. At Nicole's house, the rear gate and the walkway contained Simpson's blood. The shoe print of Goldman's shoe and Nicole's fingernails had her blood on it. At O.J.'s place, the foyer and driveway contained the same blood. The socks found in Simpson's bedroom had his and Nicole's blood on it. The glove found on his property contained the blood of all three of them. In Simpson's Ford Bronco, the instrument panel and inside door contained O.J.'s blood. The steering wheel had the blood of O.J. Simpson and Nicole on it. The carpet on the driver's side contained Nicole's blood, and the console had the blood of O.J., Nicole and Ron Goldman.

     There were five blood drops at Brown's home containing DNA that matched Simpson's, four were located on the walkway and the fifth blood drop was found in the driveway. The blood drops on the walkway began near the murder victims, to the left of the bloody footprints leading away from Brown's home and continued past the rear gate and into the driveway. The location of the blood drops indicated that they were shed by the killer, who was bleeding drops to the ground as he left the scene of the crime, heading from the walkway to the rear gate and then the driveway.

     The DNA analysis on the blood drops was conducted by the LAPD lab, Cellmark (a private lab in Maryland), and the California Department of Justice Lab. All three labs independently found that the DNA in the blood drops matched Simpson's DNA. A RFLP (Restriction Fragment Length Polymorphism analysis) was done from a blood drop found on the driveway that was large enough to be tested on through the procedure. This procedure produced a 1in 170 million match of Simpson's DNA to the DNA in the driveway. The other four blood drops were tested by PCR testing (Polymerase Chain Reaction). There was a 1 in 5,200 match on the fifth.
These five drops were among the most powerful evidence against Simpson because they represented the DNA evidence least persuasively contested by the defense. Criminalists collected the blood on June 13, 1994, prior to the time, when the police first obtained a sample of Simpson's blood. This meant that any police tampering would have involved not simply planting the evidence but substituting the evidence and it would have had to have taken police while the drops were in the custody of police criminalists. This substitution would most likely had to have taken place between the collection of the blood drops on June 13th and DNA analysis of the blood drops on June 14th at the LAPD lab. Blood smudges were found on the packaging of one of the five blood drops. This indicated that the pieces of cotton (swatches) on which the blood drop had been collected were wet when placed inside their packaging. The swatches, left to dry on June 13th, had more than adequate time to dry before they were placed in the packaging on June 14th, so a stain from wet material, when the material should have been dry, raised questions. Something wrong happened or has happened whether the evidence was tampered with or was contaminated. It was argued that the swatches might have been switched. One criminalist testified that she placed her initials on the packaging containing the swatches, but no initials were found. Besides, swatches like those on which the blood was collected were distributed to detectives for purposes of evidence collection, so that a detective intent on switching the swatches would have had the material to work with swatches to wet with blood.
Evidence could have been more than deliberately removed and replaced; it was also argued that lab procedures had so thoroughly contaminated the blood evidence that any DNA analysis of the blood would be unreliable. Extremely serious patterns of contamination in the LAPD's PCR analysis were found in other tests. The RFLP result matching Simpson from the driveway might have been contaminated, although that test was much less vulnerable to contamination than PCR. Also, the DNA analyst for the LAPD contaminated the blood drops found at the crime scene while preparing them for DNA analysis on June 14th, after getting blood from Simpson's voluntarily given sample on his lab gloves.

     One major question that arose was if the blood drops from the walkway and driveway had been infected with Simpson's own DNA by lab error. If they had, then they would have shown not only a DNA profile but also the profile of the real killer. However, only Simpson's DNA profile showed.