Ok, here's the logic:
1. The perpetrator(s) kidnap the 3 women in the wee hours.
2. The perpetrator(s) leave the house in normal condition and the dog alive inside.
3. All of the expected cars are in the parking lot.
4. So from the outside, no one would ever know that the women were missing.
5. And in fact, even though a number of calls to the house weren't returned and Janelle and Mike actually entered the house, they did not raise an alarm.
6. It's not until evening (probably 18 hours after the kidnapping) that anyone calls the police.
7. By the time police arrive, crime scene #1 (the abduction) is thoroughly compromised.
8. Meanwhile, somewhere, the kidnapper(s) have the 3 women, who are either alive and in terrible trouble or they are already dead.
9. The crime is still ongoing until the women's bodies are buried or disposed of.
10. The purpose of kidnapping 3 women is to take them to a place where the kidnapper(s) feel safe to take the crime to the next level. The kidnapper(s) need time and they do not want to be interrupted. The kidnapper(s) may be smart enough to know that murder and/or rape (the only plausible end point here) will leave a great deal of evidence.
11. Unless the kidnapper(s) are total morons, they have to know that the disappearance of 3 women, 2 of them just graduated from high school, is going to trigger a huge investigation.
12. So it's imperative for the kidnapper(s) to avoid discovery.
13. The time clock on the investigation starts officially with the first police report, but really begins when the police department gets all hands on deck in an investigation.
14. As long as it is not discovered that the women are missing, the timeline is in the favor of the kidnapper's.
15. If no one is supposed to be home, no one should pick up the phone. If no one is at the house, the investigation hasn't begun. No one is looking for the women or their bodies. No one knows anything has happened.
Now, if the kidnapper(s) are random killers, with no connection at all to Sherrill, Suzie or Stacy, then it's unlikely that the calls on Sunday had anything to do with the missing women. But the call on Friday has been characterized as "of interest," so that suggests to me that at least that call might be related to the abduction. If the kidnapper(s) knew one or more of the women, they may have wanted to see if their time had run out and they had to begin worrying about a full investigation. If one of the calls hadn't been answered by someone in the house and the other hadn't been erased, we may know more than we know now.