The private investigator's report stated Mr. Davis had accompanied subject (Donna) on an inspection tour of the apartment on September 5th 1970, and his inventory sheet is dated September 5th 1970. Also with him was Frank Desimone". Even if this was 9:00am in the morning, Donna Lass, had she set off for work at about 5:00pm that evening (for her 6pm shift), would only have been living at her new apartment for 8 hours if she was abducted outside the casino or on her way home in the early morning hours of the 6th. It would mean she had never slept at the 3893 Pioneer Trail Road apartment.
Several possibilities have been put forward. She could have been coaxed from her work station by somebody claiming they needed urgent assistance in the parking lot and abducted, or she could have been lured to somewhere within the casino, murdered, and surreptitiously removed at a later date. Donna may have been offered a lift home and murdered in her apartment by somebody she trusted, or driven elsewhere. Or she could have walked home and been abducted along the way, or the moment she arrived at her 3893 Pioneer Trail Road home. Another possibility is that Donna Lass could have arrived home safely and gone to sleep, to be murdered at this juncture by somebody entering her apartment. She could also have been murdered later, on September 6th, 7th or 8th (depending when Gordon Petrovich received the mystery call)..We could wade through all these options forever, so the best approach is to discover how the phone caller knew the name of her landlord and that her family lived out of town.

Donna inspected the apartment on September 5th 1970, accepted the accommodation and then went to work a few hours later, where she was last seen at approximately 1:50am on September 6th 1970. The only people that could possibly have known this information would have been the casino itself, or friends/work colleagues that she told between the time she signed the rental agreement on September 5th 1970 and 1:50am on September 6th 1970. This information is not going to be known by a random abductor from the casino parking lot, or a stranger snatching her from the street while walking home. We also have to factor in that the perpetrator likely knew that her family lived in South Dakota, and by making the phone call claiming a family illness out of town, he was affording himself plenty of time to cover his tracks.
If he had known Donna Lass when she moved to South Lake Tahoe in early June 1970, he had plenty of opportunity to know about her family circumstances in the intervening 3 months, but could only have learned about her new apartment and the name of her landlord from the moment she put pen to paper on September 5th 1970 to the time she was last seen. Even if he was the person who recommended the apartment complex to her in advance of September 5th 1970, it is not certain she would have accepted the accommodation until after the inspection. This information could only realistically have been known after she signed the contract.

Without access to this information, the notion that somebody would make a conscious decision to remember the spoken mention of her landlord's name (had she ever told anybody), knowing they were going to kill Donna Lass in the coming hours and then make a phone call to the casino they worked at, or frequented as one of her male friends, takes some believing. But if the person who made the phone call using the name "Mr. Davis" had access to this written information at the casino, he is in danger of drawing the police to people who worked at the casino, including himself. It is possible that this was a mistake by the killer, who was desperate to buy time by using the credible name of her landlord to deliver the message.
Somebody who knew Donna Lass had signed the rental agreement at the 3893 Pioneer Trail Road apartments and knew the landlord's name, could have been another resident at the complex. Such a person had the opportunity to abduct her if she had made it back to this location in the early morning hours of September 6th 1970 (or on September 7th/8th), but how many people at this complex would Donna Lass have told about her family "living out of town" in the few hours between signing the contract and leaving for work? In those few hours she could have spoken with a neighbour who asked where she had moved from - and at some point she told them she was originally from South Dakota. This scenario isn't implausible.

The only way Joseph Stephen Holt, responsible for the murders of Brynn Rainey (27) in 1977 and Carol Andersen (16) in 1979, could have reasonably known the name of Donna's landlord and that her family lived out of town, was if he was either in the casino on September 5th or 6th 1970 and had picked up this information by word of mouth, or had coerced this information from her for the purpose of the phone call. It's unlikely a stranger to Donna would need to force information from her to to buy time, yet somebody known to her may want to create this necessary breathing space, knowing that they could come under suspicion, Forcing information from somebody you've abducted to create a delaying phone call isn't the likeliest of scenarios, however, since we now know that Joseph Stephen Holt was responsible for the murder of Brynn Rainey in 1977, in which a phone call was made to her place of work (the Sahara Tahoe Hotel) to excuse her absence, it doesn't seem inconceivable in 1970. After all, both Donna Lass and Brynn Rainey's family lived a considerable distance from South Lake Tahoe, in South Dakota and Ohio respectively. I still doubt the involvement of Joseph Stephen Holt in the murder of Donna Lass, so if it isn't him, the focus should still remain on the Sahara Tahoe Hotel and anybody that knew she signed that rental agreement with Nick Davis just a few short hours earlier.
FURTHER READING: THE MYSTERIOUS PHONE CALL TO THE CASINO RE-EXAMINED