What should the questioner do concerning a man who gave him a sum of money to buy and sell clothes for half the profit, but he has not recovered the money or the profit after months have passed, and he discovered that he paid a larger sum in a housing association, and the questioner swore to kill him if he did not recover his money, knowing that the money is owed and that the courts are useless?

What happened between you and that person is known in Fiqh as "Mudarabah (definition)" (speculative partnership), and what is due to you from him is the money, not his killing. Killing a soul unjustly is a grave crime and one of the major sins. You are not permitted to fulfill your oath; rather, you must break it and expiate for your oath. You should employ stratagem to recover your money from him, seeking assistance from people of virtue and wisdom. If you are unable to do so, then refer his matter to the judiciary. If you are compelled to pay a bribe to attain your legitimate right, there is no sin upon you; the sin falls upon the one who accepts the bribe.