My girlfriend's dad killed our child?

my girlfriend (15) got pregnant. and i told her to keep the baby,we were happy. then i thought it was necessary to talk to some adults and i asked my girlfriend to tell her dad. she did and hours later,i called her. she didn't answer. i started to get worried. i went to her house,her dad was there and he told me he would get rid of the baby and if i had anything against he would kill me. he threatened me with a gun. i got scared and left .a day after i went to her house again ,this time i wanted to take her with me in my house but noone was home. no calls,i tried to contact her but nothing. days later she told me she had an abortion.i know she loved our child,her dad killed our baby. and now i want revenge,seriously. and i need help