[Mother]

Did we watch the same movie? Because I'm watching it now and there are no lasers being taken to the derelict. They have flashlights, that's it.

Anyway, I'll quote the section you're referring to about Ash saying the Xeno is unkillable:

RIPLEY
How do we kill it.

ASH
I don't think you can. Not
in this ship, given its life
support systems. But I might
be able to.

RIPLEY
How.

ASH
I don't know quite yet. I'm not
exactly at my best at the moment.
If you would reconnect...

RIPLEY
No way.

ASH
Don't be so hasty. You'll never
kill it without my help.

RIPLEY
We've had enough of your help.

ASH
You've barely got any oxygen left.
If you don't go into hypersleep,
you'll die with or without the
Alien.

RIPLEY
Nice try, Ash.

ASH
I will do whatever I can to help
you. I swear it.

PARKER
Pull the plug.

LAMBERT
I agree.

ASH
You idiots. You still don't
realize what you're dealing with.
The Alien is a perfect organism.
Superbly structured, cunning,
quintessentially violent. With
your limited capabilities you have
no chance against it.

LAMBERT
You admire it.

ASH
How can one not admire perfection.
I will kill it because I am
programmed to protect human life
as you know.

RIPLEY
Even if you have contempt for it.

ASH
Even then.

Bitter and angry.

RIPLEY
Sorry Ash. I don't buy it.

ASH
You egocentric morons. You'll
be ripped to shreds, destroyed
and...

Ripley make a movement.
Ash softens...

ASH
I can only wish you well...

Ripley pulls the plug.

PARKER
He was probably right. We do
need him.

RIPLEY
He was conning us.

LAMBERT
He was programmed to protect
human life.

RIPLEY
He wasn't protecting our human
lives and that's all I care about.
Anyway it's done.