Oslo killings

why they are killings innocents, violence is not the solutions of every disputes/conflicts/ differences.we know the terrorists are working under certain pressures of extremists/ their bosses are fulfilling the objects through the innocents. if killer will found so he will be prosecuted and his boss will be safe. what is the return of those who died. we do not understand that the destruction of properties and killings of innocents will not solve their issues.it is cowardly acts  of terrorist. if found guilty should be hanged till death.