The town of Arusha, in the northern part of Tanzania, hosts a small courtroom that has heard some terrible things and handed down some remarkable rulings in the world's quest for justice.

The International Criminal Tribunal for Rwanda (ICTR), established by the UN 25 years ago, tried the masterminds of the fastest genocide campaign of the 20th century.

In Rwanda, where I come from, ethnic Tutsis were targeted and nearly exterminated. Moderate Hutus, whose conscience overcame hate and turned down orders to kill or to betray their neighbors, were also killed.

More than 1 million Rwandans were murdered in just 100 days.

My aunt, a Tutsi, was killed along with her children. The killer was her own husband, who was Hutu. He killed the woman he once loved, and his own children, because he was convinced by the evil media that propagated hate and lies they [children] had Tutsi blood.

Our fellow Rwandans were massacred mercilessly. Most of their body parts were cut off and then buried alive. In some cases, militias ate human flesh and drank their blood. Tutsi women were raped.

Tribunal for Rwanda sets precedent

The UN tribunal for Rwanda heard all these stories, decrypting jargon used by killers and masterminds of the genocide.

The court indicted 93 individuals, all politicians, businessmen, military and government officials, journalists, and religious leaders.

Eighty cases were completed, and all concluded cases became legal tools in the international legal system.

It was the first international court to recognize rape as a means of perpetrating genocide.

The genocide in Rwanda was horrifying. Unfortunately, it doesn't seem to be a lesson to the international community or a deterrent to criminals across the globe.

Read more: The trauma of Rwanda's post-genocide generation

In Sudan's Darfur, the UN estimates as many as 300,000 people have been killed, but perpetrators are still at large.

An estimated 400,000 Syrians have been killed since an uprising in March 2011 spiraled into civil war. Dozens of thousands of Yemenis have also been killed since 2015.

In Cameroon, more than 3,000 people have died in the English-speaking regions. Shockingly, more than 200 villages have been burned to the ground by the military. Human rights groups and experts see what's happening in Cameroon as a Rwandan version of genocide in slow motion.

The world needs international justice systems to do their job and bring to justice all perpetrators of horrendous crimes.

There are good examples where the International Criminal Court (ICC) has intervened.

ICC interventions

The indictments of key suspects in Africa, including former Sudanese President Omar al- Bashir, served as a warning shot to a majority of criminals on the continent.

The convictions of Thomas Lubanga and Bosco Ntaganda, both former rebel leaders in DR Congo, sent an ominous signal to their supporters and African dictators that the arm of justice is not too short of reaching them.

Both the ICTR and ICC have done an incredibly good job, but they have no shortage of critics. Experts say the UN courts have held relatively few trials despite the substantial budgets.

Read more: Rwanda marks 25 years since genocide

In my conversation with Tjitske Lingsma, author of All Rise, a book that paints a grim picture of the work of the ICC, says the court hasn't managed to become relevant since it was established as it has only a few convictions — while the prosecution has lost so many cases. "With the current international political climate," she told me, "it will be harder to become relevant. Some judges haven't helped either to support reputation building, demanding a higher pay!"

While I agree with Tjitske and other critics of the UN courts, it's our duty to make sure these institutions serve in the interest of international justice and as a deterrent to crimes against humanity. The cost of impunity is higher than the shortfalls of the international courts.

For those who see regional and national courts as an alternative, I have no trust in these institutions. Most of these courts are led by the very people who have blood on their hands. Their independence is questionable — and the number of victims of horrible crimes is growing. Our biggest shot is the international courts.