It has come to be known simply as the “Speicher Massacre." But three years on, families whose loved ones were mercilessly murdered in the Iraq attack are calling on the U.S. to help them find some closure.

“ISIS called me from my son’s phone and humiliated me. They said: ‘Your son is killed and we threw his body in the river so come and get him,’ then they hurled abuses at me,” Um Hussein, the mother of a victim identified only as Hussein, recalled to Fox News from her home in a poor part of the southern Iraq city of Nasiriyah. “I didn’t hang up. I held on. I held on with the small hope that they might tell me where to find my son’s body.”

While dozens have been held responsible for the attack, the families say that’s not good enough. They want high-ranking government officials – including the former prime minister – to also be held responsible because, they claim, the officials abandoned and betrayed the mostly low-ranking military recruits killed in the attack.

On June 12, 2014, right after ISIS seized the country’s second-largest city, Mosul, the Sunni Muslim group claimed responsibility for what would become one of the country’s bloodiest single attacks on military members. As many as 1,600 unarmed Iraqi Air Force cadets outside Camp Speicher near Tikrit, the hometown of Sunni dictator Saddam Hussein, were massacred.

Part of what made the massacre so stunning was that ISIS had yet to take official control of Tikrit; after all, Tikrit lies 150 miles away from Mosul where the bulk of the ISIS fighters were celebrating a fresh victory. Yet, despite the distance from Mosul, ISIS was able to slaughter hundreds of Tikrit’s young men.

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“ISIS supporters and sleeper cells were ready and came out, taking advantage of a security vacuum,” Col. Mohammad Abdullah, a high-ranking Iraqi military officer, explained. “What happened was a response to the hidden hatred that was buried inside those close to Saddam’s personal guards. They found themselves without jobs or authority after 2003. Their hatred led them to act in revenge.”

The fateful day began calmly enough. The cadets, who were unarmed, were starting a break and walking along a road to their homes. Two buses -- one driven by a son of Saddam Hussein’s half-brother -- pulled up near the cadets. The men inside the buses said that they were from local Tikrit tribes and would assist them in getting to Baghdad. Instead, the cadets, mostly between ages 19 and 25, were kidnapped, taken to the Al-Qusour Al-Re'asiya region and one-by-one killed. The assailants made a particular effort to kill Shiite and non-Muslim cadets.

ISIS subsequently released videos of the massacre, showing a line of young recruits blindfolded, tied-up and marched to what would become their own mass graves in the desert. Photos of cadets being beheaded, having entire magazines emptied into their heads or being strangled to death against the fanfare of jubilant militants became fodder for online ISIS recruitment.

For 10 months after the slaughter, families had no word of what happened to their sons, nephews, husbands and cousins. Iraqi forces finally re-captured the base from ISIS in March 2015, and some family members were able to give DNA samples to assist authorities in identifying the bodies. But still today, a large portion of families are begging for answers.

“I still see him in my sleep, my son tells me not to cry and that he is in a better place,” Um Hussein noted softly, with the type of hoarseness that can only be felt by a mother that has lost her child in the unknown. “But I can’t change his bed covers, nobody can sleep in his bed because maybe he will come back one day.”

The Iraqi government eventually blamed both ISIS and members of Saddam’s dismantled Iraqi Ba’ath Party for the killings, but by then some alleged perpetrators had fled. In late 2015, two suspects were arrested in Finland, having been identified from the propaganda videos. The Finnish government denied an extradition request from Iraq, and instead the twin brothers were acquitted on all charges this past May.

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And last August, the Iraq government – despite opposition from human rights groups – sent 36 people to the gallows for taking part in the massacre. But that is far from justice for many left in anguish. According to military official Abdullah, “The authority figures in charge have not been charged due to political reasons. To avoid having to go after ‘large figures,’ the investigation barely touched the surface.”

“There were huge political and administrative mistakes such as sending young military cadets to train in an area that was not safe, and left them without weapons or commanders and communications,” he said. “What needs to happen now is a real investigation that is unbiased, with the help of foreign specialists. Without charging the terrorists and also the authority figures who were in charge, will leave a huge gap among the Iraqi people and make the national reconciliation very hard.”

Earlier this month, on the third anniversary marking the day the horror, demonstrators swarmed through Baghdad’s Tahir Square and called for the prosecution of former Prime Minister Nouri al-Maliki for his failure in leadership and demanded he take responsibility. Maliki, now one of three vice presidents, and is believed to be building his support base to regain the premier post once again.

“These soldiers went to Tikrit to protect the people and were instead betrayed by the people there. They were sold out to ISIS by local tribes. They were told that they would be helped to get back to their families but instead were handed straight to ISIS,” Mohammed, who hails from the south-eastern Iraqi town of Amarah and lost his brother in the Speicher massacre, lamented. “Every commander all the way up the chain to the prime minister’s office bears some responsibility for this. We want legal charges against every party responsible.”

He, too, is calling on the U.S. and international community to help them re-open the case.

“It has been three years and the majority of families don’t know what happened. We don’t know who was working and coordinating this attack with the new (post-Saddam) Iraq government,” Mohammad added. “This massacre has become a wound that won’t close. We feel like our brothers and sons were sold out in a political bargain between corrupt officials and that is why they are trying to hide and close it forever.”

Last week a spokesman for Inherent Resolve said in an email to Fox News that the Speicher massacre was "an internal matter for the government of Iraq."