Blood found on the gate of Nicole Brown Simpson's condominium, which prosecution tests have matched to O.J. Simpson, was not collected until three weeks after the murders, Detective Tom Lange told the court today. On his third day of testimony, Lange reported that he had asked a technician to gather the evidence the day after the June 12 murders, but his orders were not carried out until July 3, after the crime scene had been unsealed and open to the public. Pressing his argument that police mishandled the investigation, Defense Attorney Johnnie Cochran suggested that curious sightseers could have contaminated the blood sample. Kato Kaelin, O.J.'s houseguest the night of the murders, is expected to testify Thursday.