Defence lawyers began questioning police criminologists over the handling of the blood, which was found near the bodies of Nicole Brown Simpson, 35, and Ronald Goldman, 25, who were stabbed to death outside her townhouse in an exclusive neighbourhood in June.
The issue has become one of considerable significance, as it was disclosed on Monday that the preliminary results of DNA tests had established that a drop of blood containing identical genetic markers to Mr Simpson's was found at the murder scene. This strengthens evidence given to a preliminary hearing in July that initial tests - also based on DNA - had matched Mr Simpson's blood to drops found in his car, the foyer of his house, and a blood trail leading from the bodies.
But it was also the same as the likely blood type of between 40,000 and 80,000 others in the metropolis. When completed, the more recent tests - RFLP analysis - will reduce the odds of a match with someone other than Mr Simpson to a million to one.