Brianna is walking along, completely unsuspecting what is about to
happen to her.  Elizabeth, holding a water gun, "shoots" Brianna.

The detectives, Vanessa, Gina, and Dorothy, arrive on the scene.  

Gina:  Is she alive?
Vanessa:  I can't tell.
Dorothy:  Take her pulse.

Gina bends down to take Brianna's pulse, but she is wearing a
scarf and it's all tangled around her neck.

Gina:  I can't; her scarf is in the way.
Dorothy:  Here, try this.

Dorothy hands Gina the laser.  

Gina:  What is this for?  
Dorothy:  If a person is alive, the laser will shine through one
of their fingers.  If they are dead, you won't be able to see
anything.

Gina shines the laser through Brianna's limp finger.

Gina: She's alive!

Vanessa (To the audience):  There are many applications for
lasers and optics in forensic science.  In this next example, a
laser is used to pinpoint the location of the suspect when she
shot Brianna.

Dorothy:  When I stand here, the laser is perfectly in line with
the bullet hole.  This is the same spot where the suspect was
standing.

Gina (points to the water gun):  This must be the weapon!

Gina walks over to the gun and explains what she is doing while
she is demonstrating.

Gina: When I brush this powder on the gun, the fingerprints
become visible.  When I shine an ultraviolet light on it, they
become more visible. To remove one of the fingerprints, you place
one of these strips onto the fingerprint.

Dorothy (shines blacklight onto wall):  Look! a message! (Reads
message)

Vanessa:  Our suspect has used a crayon that only becomes visible
when ultraviolet light is shined on it.