Any dogs can be 'killers'.. I had a shit-zu X maltese, and it was a complete psycho! And attacked soo many people.. It wasn't the way I brought her up, it was because when my sister was walking her, two other much larger dogs attacked her, because their gate was open, close to her death. And she was my dad's little angel after that, when she started going a bit crazy from the attack. Then my dad passed away, and the dog was un controllable.. Could not help the dog no matter what we tried, she attacked so many people, old and young- it was so heart breaking because before all the trauma she was an amazing dog..
Now ive got a rottweiler X bullmastiff, and he is AMAZING, a complete gem.. He got out of the house one day- cos he's unbelievably sneaky haha, when my mum was leaving the house he just quickly quizzed passed out the front door, and got slightly hit by a car, no stitches were needed but boy it shocked him, REAL bad.. he's now scared of cars, and when i walk him on main roads he hides between my legs with his tail between his legs,but even though has fears, he still is not violent and has never hurt anyone, attempted to hurt anyone, or any other animal, he's still totally gentle.
So having 2 complete different dogs, and them be so strangly different- I strongly believe it has NOTHING to do with the breed, it is just it's way of coping with bad things that happen- not just the way its brought up. Because i called the rspca on a dog that was never fed, was hit, recieved minimal food every few days, and completly ignored- which i believe is the worst crime to a dog, they need so much love.. and this dog ended up being a GREAT pet, i used to walk him to get him out the house and he is such a beautiful beautiful dog.. and he is also, a pit bull.. and he is now is a great home, being treated very well, and although the way he was brought up was terrible- he is still an amazing dog with a beautiful temper!