The time of the murder has been estimated between 9:15 pm and 10:45 pm, based on eyewitness reports and autopsy findings. One woman from a nearby residence stated that about 10:30 pm "I heard a muted scream, and then a loud sound like an old car being started up - this was about two minutes after I heard the first scream". Other eyewitnesses would corroborate the time between 10:15 pm and 10:45 pm, suggesting that the idea people failed to adjust for daylight savings, sending the clocks back the previous midnight, highly unlikely. Placing the murder at 9:15 pm sounds more plausible based upon the fact the library closed at 9:00 pm, however, considering Cheri Jo Bates arrived at the library shortly after 6:00 pm, this places her in the library for nearly three hours, yet only one person definitively stated that he saw her in the library during the entire evening.
Cheri Jo Bates' liver temperature was recorded as 26C and 28C at 9:31 am on October 31st 1966 at autopsy. Algor Mortis is the rate at which a body cools after death - very little during the first hour, but calculated thereafter at 1.5 degrees Fahrenheit per hour, dependent on ambient temperature, body size, clothing etc. The temperature in Riverside that day hit a maximum 97 degrees Fahrenheit, falling to 52 degrees Fahrenheit at its lowest, giving us an idea of ambient temperature during this period. There was also little to no wind at this time, therefore not adversely affecting the rate of body cooling. Taking normal body temperature of 98.6 degrees Fahrenheit and Cheri Jo Bates median liver temperature of 80.6 Fahrenheit at 9:31 am, we can calculate the approximate time of her murder,
The body of Cheri Jo Bates had cooled by 18 degrees at autopsy, but not counting the first hour, this would take 12 hours (18÷1.5). Then if we add back the first hour, it gives us a time period of 13 hours. This would mean Cheri Jo Bates was murdered at 8:31 pm or slightly earlier, as body cooling actually slows down in rate, as it approaches the ambient temperature. If we take the high end measurement of her liver temperature of 82.4 Fahrenheit at autopsy, it places the murder at 9:31 pm, or again slightly earlier, bearing in mind the existence of a "temperature plateau", a highly variable length of time in which the body does not cool.
Joseph Bates arrived back at the 4195 Via San Jose residence around 5:00 pm, finding the note left by Cheri Jo Bates "Dad-Went to RCC Library". Cheri was spotted at the RCC Library around 6:15 pm.
This is crucial, because the pathologist F. Rene Modglin stated "the gastric contents suggest she had eaten a supper type meal probably not more than 2 to 4 hours before death". In addition, the stomach contents contained "at least 100ml of thick fluid, with particulate food particles in which are easily recognized reasonably large pieces of beef, along with vegetable particulates and/or celery and onion, and what appears to be milk or cottage cheese". Cheri Jo Bates consumed this meal prior to 5:00 pm, before Joseph Bates arrived home.
Food takes approximately 2-5 hours to leave the stomach, depending on its constitution. The pathologist stated she had eaten not more than 2-4 hours before her death. This means that if Cheri Jo Bates ate this meal at approximately 4:30 pm, then she would have been killed at 6:30 pm to 8:30 pm, tying in with the findings of body temperature above - and the indication of an earlier murder. This would match the 'Confession' letter on November 29th 1966, if Cheri Jo Bates arrived at the library at 6:15 pm, checked out her books immediately and was followed to her vehicle, before being killed around 6:30 pm. The author stated "Miss Bates was stupid. She went to the slaughter like a lamb. She did not put up a struggle. But I did. It was a ball. I first cut the middle wire from the distributor. Then I waited for her in the library and followed her out after about two minutes. The battery must have been about dead by then. I then offered to help. She was then very willing to talk to me. I told her that my car was down the street and that I would give her a lift home. When we were away from the library walking, I said it was about time she asked me, "about time for what ? ". I said it was about time for her to die".
However, this throws up an unlikely scenario, that 65 people entering and leaving the library that night between 6:00 pm and 9:00 pm, would fail to spot the stricken Miss Bates lying in the driveway for at least 2 1/2 hours. Even if the murder occurred at 7:30 pm or 8:30 pm, we still have a problem - particularly in light of screams being heard at 10:30 pm at night by local residents. Additionally, we have the female eyewitness who allegedly spotted a man smoking in the alleyway at 9:30 pm, and Cheri Jo Bates' body not being viewed. But a 10:30 pm murder leaves us back where we started, four long hours to explain, and seemingly contradictory to the body temperature and stomach contents analysis.