oklahoma jury convicted 17-year-old chancey allen luna of first-degree murder in 2013 killing of christopher lane .
luna is expected to be sentenced to life in prison without parole .
oklahoma teen shot lane , an australian baseball player , in the back from moving car as victim was jogging in duncan august 16 , 2013 .
defense claimed luna only meant to scare lane , not kill him .
convicted killer told reports he was ` sorry ' as he was being led out of courtroom in handcuffs .
lane 's mother , donna lane , said she was glad the ` naughty boy ' will never hurt anyone again .