I believe the serial killer theory is possible.
Yesterday, I heard an interview with a woman named Jeremy Brown, who was a victim of serial killer Reginald McFadden. At the last minute, he decided let her go. He ambushed her, bound her, beat her nearly unrecognizable, raped her repeatedly, and then took her to the spot where he killed others. When he started choking her to death, she managed to whisper,
"Why are you doing this? You're hurting me." And just like that he stopped, put her in the car, and drove her home.
(you can listen to the interview here:
https://www.thisamericanlife.org/radio-archives/episode/604/20-years-later )
The perpetrator was a psychopath, so compassion was not a factor his decision to release her. He claimed that he
meant to kill the girlfriend of a man he'd killed two weeks earlier, but went to the wrong house. In transcripts of an interview with him, he said:
"She had no connection to Robert. So, I decided to release her. I figured she didn't know who I was, she didn't see me, you know what I mean? And I released her... Yeah, I knew she was going to go to the police."
(His victim did not have a girlfriend.)
But he also said in the same interview, "She told me she was a counselor. That's what saved her life. She talked to me. I mean, she talked me down."
(
http://mreplay.com/transcript/crimi...ller)/5304/MSNBC/Sunday_July_11_2010/366554/)
Whatever the reason he released her, it says that it is possible for a victim to be released. He had forbid her to look at him, and also put a towel over her head, but she had managed to take a peek at him without him being aware of it. If he thought she'd seen him, there's no doubt he would have murdered her.
As we know, serial killers do work in teams sometimes, and some SKs are women, and some release their victim, so it is possible SP was the victim of serial killers.
ETA: The only problem is the length of time SP was held. Do SKs ever keep a victim for 3 weeks?
I just answered my own question. As long as 6 weeks, according to the book, "
Serial Killers: The Method and Madness of Monsters"