It has been exactly one month since my fiance, the celebrated journalist Jamal Khashoggi, entered Saudi Arabia’s consulate in Istanbul never to return. Today is also United Nations International Day to End Impunity for Crimes against Journalists. The coincidence is tragic and painful. Until a month ago, Jamal sent me articles that he was writing. I would enthusiastically read them and then call him with my thoughts. He would listen attentively, and then we would debate. But now I am writing about him and how I feel now he is gone.

I am really finding it difficult to comprehend whether it has been a month or a lifetime since I lost Jamal. As I waited in hope that he would come out of the consulate, every hour, every day, felt like a year. They have been filled with anguish. No matter how long I waited, the joyful Jamal did not return. All that came was news of his death.

As I write this, Istanbul’s chief public prosecutor’s office has made an official statement. They strangled Jamal and dismembered and destroyed his body. How brutal, barbaric and ruthless. What crime did he commit for them to do this? What was the reason for them to murder him so brutally? There is no explanation for this hate.

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It is important to remember Jamal, the person. A man of kindness, patience, generosity, compassion and love. All he wanted was a fresh start to ease his longing for his homeland. To live a lonely life with some happiness. And on this journey I would have been a companion and friend. I hope he knew just how precious it was for me as well to begin a new life with him.

Jamal’s brutal murder has shaken the world. That is because we have lost a globally significant voice. Above all, he championed goodness and decency. He helped us understand the complex relations of the Middle East, but always put the lives and rights of its people first. Now in death, the principles for which he so passionately fought in life have been brought into the limelight: democracy, freedom and human rights; the fundamental belief that every person should choose their political masters through the ballot box. As we witness the international outrage at his killing, the perpetrators should know that they can never erase his vision for his beloved country. They have only emboldened it.

It is now left to the international community to bring the perpetrators to justice. Of all nations, the United States should be leading the way. It was founded on the ideals of liberty and justice for all, the first amendment enshrining the ideals personified by Jamal. With this tragedy, the Trump administration has taken a position that is devoid of moral foundation. Some have approached this through the cynical prism of self-interest – statements framed by fear and cowardice; by the fear of upsetting interstate deals or economic ties. Some in Washington are hoping this matter will be forgotten with simple delaying tactics. But we will continue to push the Trump administration to help find justice for Jamal. There will be no cover-up.

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Today I am inviting the international community to take serious and practical steps to reveal the truth and to prosecute those involved in a court of law. And to deliver Jamal’s body, which is still missing, to his loved ones.

I am not naive. I know that governments operate not on feelings but on mutual interests. However, they must all ask themselves a fundamental question. If the democracies of the world do not take genuine steps to bring to justice the perpetrators of this brazen, callous act – one that has caused universal outrage among their citizens – what moral authority are they left with? Whose freedom and human rights can than credibly continue to defend?

We are now going through a test of humanity. And it requires leadership. The biggest responsibility lies on the heads of the governments. My president, Recep Tayyip Erdoğan, and everyone in the political, legal and judicial branches of Turkey are managing this matter in the best way possible.

So I invite the leaders of all European countries and the US to pass this test. Justice must be served. I demand that those who committed this premeditated and savage assassination are brought to justice. Those who ordered this murder – even if they stand in the highest political office – should also be prosecuted. I demand justice for my beloved Jamal. We must all send a clear message that authoritarian regimes cannot kill journalists ever again.

Jamal had just bought a house. He had a dream to build a family. He was selecting household items with excitement. His shirts had just been given to the dry-cleaners on his return from London.

Yet I am left at the door alone. I am the one story Jamal did not complete. Now everyone, together, must help finish it, and carry the torch of Jamal’s soul until his dream is realised.

• Hatice Cengiz was the fiance of Saudi journalist Jamal Khashoggi