Locked Room Mystery

There's been a murder
In a locked room.

The killer didn't enter
The killer didn't leave
Where is the killer?

The killer is still inside
You see.

The murder occured
1 hour ago
At 7pm
Its now 8pm
It took me a hour to get here.

The door is locked from the inside
Nobody could of known

The killer phoned it in.

I notice, the air vent has six screws
One of these screw is rusty.
Which means one of the screws doesn't belong.

He got in through the air vent.
The screw's are put back in place.

He's not leaving.
He's staying here.

So the Question changes?
Who benefits?

I enter the room
The room is empty
But Where is the body?

The body hasn't been moved.
Not even touched.
The untold merits of death
Have not even been discussed.

Answer
I'm the body
I'm the Victim
A puzzle to solve
As this plot thickens.

The clock is Lieing
The little hand is on the 7 not the 9
Which means it's 7.pm
The time of death is now.
He strikes.

She pulls a knife.
I pull a gun.
Guess who strikes first?

He dies on the floor
In front of me.

I try to escape
Through the air vent.

That leads me outside
Into a situation I tried to prevent.

The police arrive
And charge me for murder.

The dead tell no lies
But no one can hear her.

So you see
She was the Victim
I was the killer.

A role reversal
A mystery
A thriller.

But who benefits?