Time travel

An astronomer named Crime
Travelled back in time,
And left his grandpa dead
Shooting him in the head.
Now grandpa is no more
From his very early age,
So mama is not born,
Not yet, at this stage,
To give birth to Crime
That travels in time.
Will grandpa resurrect
Now that Crime is gone,
To give birth to his daughter
From whom Crime is born?
[If grandpa comes not back,
Looms a daunting task:
Who is to blame for the crime
Of traveling back in time?]