Do report him to the police..... he did the crime, you have every right to have it investigated.
Id had the nastiest stepdad too (my Mum divorced him in March this year
)
He was violent to me too (and i got police involved at the time and he was charged and has it on his record etc
) and was emotionally abusive to my mum.
Always adament that she was HIS, and he would never EVER "let" her leave him.
And for 15 years he suffocated her personality and made her scared to leave him (or upset him) etc etc
If he didnt get his own way he always threatened to kill himself, and my mum was stupid enough to believe him 
Anyway after he attacked "if I went to the police he was going to kill himself, it would ruin my mums life and she would hate me for ever and ever for making him die" (his words to me.... [hmmm])
SO.... I told him "Go Kill yourself, see if i care, my mother wont have to divorce you if you are dead"
and off i went to police.... (and unfortunatley he didnt kill himself)
Next time i saw him i greeted him with "Oh i thought you'd be dead by now?"
Finally my mum saw the light and left and divorced him...
I sent him a card "On the loss of your wife" 
Thats all it said, and a pic of a flower
Inside i wrote
"I told you she'd leave you one day, yet again i was right
"
It did not go down well, as he "told my mum" lol, as if i could care less.
He also sent his mum round to tell my grandparents that I had ruined his life LOL, and to tell my grandparents that actually he has never touched me
..... at the end of the day my granparents had seen the 7 bruises he gave me, told them to bugger off, and we have never seen them again, thank god.