You have 3 options. You may lodged a complaint or blotter with any nearest police station. If he is a foreigner, the police will give him a visit together with your complaint. If the respondent will not own up, they can file your complaint with the prosecutors.

If the respondent is Qatari, you go to the Ministry of Human Rights and they will assist you there.

You may also try your embassy which normally have legal officers familiar with local criminal procedures to assist you.

Good Luck.