WHY did the police KEEP Sidney in Woodsboro?

That's one thing that annoyed me too... it just seemed like lazy writing during the rewrites while they were shooting.

In the first shooting draft of the script that scene wasn't there and it was originally Sidney and Rebecca were leaving Woodsborrow after spending the night at Jills -

INT. LIVING ROOM - ROBERT’S HOUSE - NIGHT
Rebecca and Sidney are in the living room with their luggage.
REBECCA
I had reservations at the
Doubletree.
SIDNEY
It’ll be better here. All of us in
numbers. We’ll be safer.
REBECCA
As long as we’re in Seattle by
Tuesday. So what’s the deal with your Aunt? Where’s Jill’s dad?

But then Olivia was killed and they end up at the hospital -

SIDNEY
He told me to leave town as quickly
as possible.
GALE
He did?
SIDNEY
He said the next STAB movie was
about the death of Sidney Prescott. I interpret that as: Get the hell out of town now.
REBECCA
Good. You’re okay. Cuz’ there’s
tons of press requests...
SIDNEY
We’re leaving tonight. We’ll drive
to Oakland and fly standby. Where’s the rental?
REBECCA
In the lot. There’s a lot of press
out there. Let me pull the car up. I’ll text you.

But then Rebecca's death scene happens -

INSIDE THE CAR
MAN’S VOICE
Please let Sidney know it’s
imperative that she not leave town and to illustrate this I’m going to kill her assistant.
REBECCA
Excuse me...?


Sid’s CELL PHONE RINGS. The CALLER ID says Rebecca. She picks it up.
SIDNEY
Bec? Are you out front?
MAN’S VOICE
Yes, Sidney, you’ll find Rebecca
right out front.

Then she decides to stay to protect Jill and with the hope Ghostface won't kill anyone else just her -

GALE
This isn’t your fault, Sid.
If anything it’s mine. I wrote the book, I sold the movie rights. I started this.
SIDNEY
You’re right. It is your fault.
But I knew better. (then)
Now, I can’t leave. We have to keep her safe.
Sidney is referring to Jill.
GALE
We will.
SIDNEY
I don’t care what happens to me.
But no one else can get hurt.

Someone's trunk is a murder evidence factory, and they should just be allowed to go on their merry way because they happened to be attacked a decade before? I'm not sure I agree 100% with your police work there, Lou.

---
Kieran is a retcon. Audrey was Piper's original partner.

Police operate on preset procedures, not film logic (even if the latter is often the wiser course).

I agree it is stupid but I guess that's standard law enforcement procedure. I'm more baffled as to how Jill and/or Charlie put the evidence in Sidney's car without anyone knowing; especially since it's a rental car and you would have to assume that Sidney stopped at the house before going to the book store; that's the only time they could have put the evidence in the trunk. But Kirby picks up Jill and Sidney is already at the book store so when did they put the evidence in the car? Very sloppy writing which is what this entire movie is full of.

I would have cut the whole scene with the evidence in the car and have Dewey tell Sidney that he needs her to stay in Woodsborn in the same tone as when he tells Gale in the first one, "You're not scared, are ya?" The sinister music plays when Dewey says that and the audience suspects him. Why else would he need Sidney to stay here? As the audience, we think it could be that Dewey is the mastermind of the new killings. Realistically, I'd hate to have Dewey or Gale as the killer but it gets the audiences mind going. I felt they never did the red herring in this film like they did in the others. The real reason Dewey wants Sidney to stay is to protect her family.

Love how the post was mostly just rehashing the series.

Anyway, they lightly explained it in the film, and to the best of my knowledge, it was realistic. The stuff was put in Sidney's trunk because that made her a material witness, and even though no one actually suspected her, it did legally require her to stay, as she was tied to the case. Beyond that, the fact that she'd previously been attacked so much doesn't guarantee she's not the killer, maybe she finally snapped and this is it is how they'd see it.

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Some BS theory that Sidney finally snapped and she started killing folks. The only person from Woodsboro is Billy's father who could be a suspect. I mean his son and wife were killers. Sidney has done a great job holding herself together after 15 years. That is one of the reason why I love the character. Sidney is a strong woman. If the franchise continue with Scream 5 would be happy if Sidney never returns she deserves it after everything she been through.