It seems on the face of it to suggest the phone caller is buying time. They appear not to want any police involvement immediately, and since family, friends and associates are usually the first port of call for investigating officers, this is who would benefit most from any investigative delay.
The perpetrator/s most likely had a vehicle parked outside the Sahara Tahoe Hotel, Abducting a woman at a busy casino and hotel by dragging her away on foot is extremely unlikely and far too risky. Whatever happened subsequent to this is in the realm of speculation, but one reason to want to buy time in the following days, can be attributed to a forensic standpoint. Had Donna Lass been taken to a second location connected to the abductor, or attacked within the confines of the assailant's vehicle leaving trace evidence, then clearly this provides good reason for the perpetrator to want the clean up before the police come knocking. A murder distinct and separate, leaving nothing of forensic value to connect to the perpetrator, does not necessitate the further risk of identification through a phone call. The phone call itself provides another clue. If Donna Lass had driven to work on the day in question, her car would have been laying dormant in the casino car park, so an anonymous caller claiming she had been called out of town on family business, could easily have raised suspicion from her employers, and simply negated the caller's intention of buying time. In fact it would have had the opposite effect. The same could be said regarding the landlord of the Monte Verdi Apartments, if the landlord was familiar with her vehicle or was regularly present on site.
Her Chevrolet Camaro parked outside her Monte Verdi Apartments and the apartment itself, showed no signs of foul play or disturbance. The likelihood is she disappeared from the vicinity of the casino at around 1.45 -1.50 am and unlikely from her nurses station, as this would have attracted too much attention. As Zodiac researcher Raymond Grant has already stated, the likeliest scenario, is Donna Lass was enticed away from her work station close to the end of her shift in a planned abduction, performed under the guise of a medical emergency, that not only explains the abrupt pen mark trailing off her log book, but is the perfect ruse to necessitate her separation from the confines of the building and into the darkness. She is bundled into the abductor's vehicle with relative ease and is never seen again.
The phone call after the Donna Lass abduction is not unusual to Zodiac and neither is the mailed correspondence, but the nature of the crime is, along with the purpose of the phone call. His previous two phone calls were designed for menace and taunting, whereas this call had the sole design to create breathing space, indicative of somebody connected to the victim and area. Of course Zodiac could have been resident in the area, known Donna Lass and been the abductor. But from what we know of Zodiac's confirmed attacks, by all accounts, he attacked strangers at a specific location and never abducted them.
The phone call in the case of Donna Lass was designed to misdirect for a reason, and quite possibly the Pines Card was mailed for the same purpose;- the first to delay the focus and the second to take the focus away. This time the perfect fall guy would be Zodiac, but one killer may have been responsible for both and it may not be the killer we have been tracking for nearly fifty years.