How can I write a narrative paragraph that uses dialogue?Begin with a 2-3 sentence description of a crime scene. How can I add 6-8 lines of...

Narrative writing first establishes setting
(place and time) and point of view, first or third person.  Your reader
needs to know where the crime has taken place, when the crime took place, and who is
there now investigating it.  As you say, it should all be done in 2 - 3 sentences.  Pick
a unique location for your crime scene and describe the place spatially, by physical
area, showing the blood last:

readability="7">

As the two detectives pried open the meat locker
door, the hanging shanks of beef guarded a secret: a severed human
head.

Then,
jump into the action by having your characters speak first (describe them
later).  You will want to start "in medias res," in the middle of the
action.  Start with a couple of detectives who are foils (or opposites): one old and
cynical, one young and naive.  You know the types, like Morgan Freeman and Brad Pitt in
Se7en.  Something like this:

readability="12">

The white breath of the younger detective
quickened in the cold as he saw the blood congeal on the floor.  This was his first
assignment with his new detective badge, and his partner, who would be retiring at the
end of the month, only laughed it off.  "Guess who's not coming to dinner," said the
veteran.

And then keep going
by building suspense.  Maybe have one of the detectives
recognize the head.  Keep the dialogue short, simple, and funny.  Like a text
message--except, you know, spelled correctly.