VALENCIA, Venezuela -- They died side-by-side when flames tore through an overcrowded police station jail in Venezuela. Many of them are being buried side-by-side, too.

Weeping relatives arrived at the central cemetery in the industrial city of Valencia on Friday carrying the caskets of many of the 68 victims who were killed in the fire to place them in a freshly dug mass tomb.

Cemetery workers said they were prepared to bury at least 32 people two days after the blaze in three-deep graves separated by a layer of cinderblock. Simple white crosses with their handwritten names, dates of birth and shared death date were put around the tomb.

"How am I going to forget seeing my husband burned?" asked Wilca Gonzalez, 36, whose husband was the first to be placed into the ground Friday. "How can you forget that?"

The mass burial comes as relatives, human rights advocates and international leaders are pressing Venezuelan officials to provide a full account of what happened and hold those responsible accountable. Aside from confirming the death toll on Twitter, officials have been largely silent and have not yet explained how one of the worst jail fires in the nation's history took place.

"I want to know who is responsible," Gonzalez said, though she said she had little hope for justice.

Varying versions of the tense moments leading up to the devastating fire are circulating among relatives and advocates, with some accounts suggesting that the inmates themselves started the blaze in an attempt to escape. At least one family member contends their relative called and claimed that guards were pouring gasoline in the cellblock before the flames began to spread.

Chief prosecutor Tarek William Saab, a close ally of President Nicolas Maduro, said four prosecutors were being assigned to investigate the tragedy and pledged a "thorough investigation to immediately shed light on the painful events that have put dozens of Venezuelan families in mourning."

As Venezuela struggles with an economic crisis worse than the Great Depression, advocates say prisoners face especially dire conditions, going hungry in increasingly crowded cells. Inmates also frequently obtain weapons and drugs with the help of corrupt guards. Heavily armed groups control cellblock fiefdoms.

The United Nations' human rights office said Thursday it was "appalled at the horrific deaths" and urged Venezuela to quickly address concerns like judicial delays, the excessive use of pre-trial detention and cramped quarters that can lead to riots and violence.

The incident is one of the worst mass casualty events at Venezuelan prisons and jails, but is not the first. A fire at a prison in the western state of Zulia killed more than 100 inmates in 1994. In 2013, 61 people died and over 100 were injured, mostly from bullet wounds, during a riot in Barquisimeto.

An estimated 32,000 detainees are being kept in Venezuelan police stations that are filled far past capacity, according to A Window to Freedom, an advocacy group that monitors conditions at the nation's jails. The jail at the Valencia police station was built to hold 35 detainees, but at the time of the fire some 200 people were believed to be inside.

Despite Venezuelan laws mandating that detainees be held for a maximum of four days after an initial arrest, relatives said many of the Valencia prisoners had been jailed for far longer, waiting to be transferred to larger facilities. Many had been imprisoned on suspicion of relatively minor crimes and had not yet gone before a judge.

The family of Gonzalez's husband, Erickson Zapata, 23, said he was wrongly jailed with several others suspected of robbing a cellphone. They said he should have been detained for no more than 10 days but instead had been in the jail for 10 months. He was kept in the largest part of the facility with 60 people crammed inside, many sleeping on makeshift hammocks from bedsheets.

Gonzalez said the last time her husband called her from inside the jail, he was pleading for help.

"I can't breathe," he cried. "I'm suffocating."

She identified his body by his crooked left ring finger and his uniquely large front teeth.

On Friday, his father, Jesus Zapata, 42, stood next to his son's casket holding his bible. With three other men, he helped lower the coffin into the ground.

His quiet sob turned into open crying as workers covered the coffin with planks, preparing the grave for the next inmate to be placed on top.

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Associated Press writers Fabiola Sanchez in Caracas, Venezuela, and Christine Armario in Bogota, Colombia, contributed to this report