Moral Hypothetical Question?

Lets say a man (call him Al) bribes safety inspectors for rides at his amusement park, then there is an accident caused by his negligence and about 50 people die and 50 more get hurt. A father of 3 children who died is upset when Al is released on a technicality and suffers no legal penalty. Is it wrong for the father to hire someone to kill Al? Is the man he hires wrong for killing him as well? Is there ever such a thing as justified killing? If there is then what must the cirstances be? Would it be wrong if Al only killed 1 or 2 people? Your input is appreciated