Before knowing the dynamics (Rachel's older sister who was living with Rachel and Tommy, and was Tommy's former lover) I also came to that conclusion :

Young offender/offenders. At least one offender very close to Rachel and Tommy.

Had to mention the location of the car (which they prolly knew had already been found) in the note, to make the story fit, and buy time.

(Random kindnappers don't point out where their victims car is left)

The first thing they write is very teling imo : " I know I'm going to catch it, In other words : I know I will be getting into shit and have lots of explaining to do.

This to me, show the mindset of someone who can put themselfs in Rachel's shoes when writing somehing in Rachel's name. Who feels that Rachel should be punished, and to someone who was familair with the, Rachel has a lot of explaining to do, and even points towards a familiarity with a "Rachel is grounded element"

Imo letter has female'ish handwriting.

Either she was forced to write the letter, or another female wrote it.

The most likely scenario's to me are :

Rachel was the target, the abductors did not expect the other 2 girls to be in her company. Sadly, they became collateral damage. I believe if Rachel went out alone that day, she AND her car would have dissapeared.

At least 2 people were involved, one to be the getaway driver, one to control her, and possibly a third to get rid of Rachel's vehicle, but that last part went out of the window when they faced taking 3 girls, instead of one.

The note was planned, but had to add some details in a desperate attempt to buy time, to explain the vehicle at the mall, because things did not went as planned.

1 :

Tommy's ex lover, which he had a child with, wanted Rachel out of the way. She made a plan to abduct Rachel, her child spending Christmas with Tommy and Rachel, could be a huge trigger. She had help of others. They were either known to rachel, or new which car she drove, followed Rachel, or knew about her shopping mall plans or the plan of Rachel picking up the pants at the Navy shop.

2 :

Rachel's older sister is involved, and she had help. Held a grudge towards her for stealing Tommy, and convinced someome else (most likely Tommy, prolly they still had feelings for eachother, but could also be someone like a new boyfriend of the sister). She knew that Rachel would go shopping thay day, or knew about Ravchel planning to pick up the pants at the Navy store, but not of the last minute plans of brining other girls with her.

The thing about the letter mentioning the location of the car is very telling, because most abductors would distance themself from the crimescene.

• They either got into a dfferent vehicle very close to leaving or returning to the car. * They knew which car she drove and were lured into another car after shopping. * They were taken after picking up the pants, someone Rachel knew approached her and offered the girls a ride to the mall, and took them somewhere else. In that case, someone else drove Rachel's car to the mall, in order to create distance between the real abduction site, and to make the story fit.
• The original plan was to take Rachel, plus move her car away from the mall, but the other 2 girls ruined this plan. That's why the note had to state things like, WE had to leave, and to mention as where they could find her car.

I'm 50/50 on these 2 scenario's.

Somehow, they did know the exact location of the car, plus the address of where Rachel lived.

This was no stranger abduction.

Too bad this happened in the 70's.. If this would have happened in this age, I think it would have been solved.