The first democratically-elected president of Egypt who after being elected in 2012 was deposed in a military coup the following year, six years later died in an Egyptian prison.

President Mohamed Morsi, who was charged by his military captors with terrorism and spying and was imprisoned and sentenced to death, was treated so badly that a group of independent UN human rigfhts experts have concluded there is "credible" evidence his death in June this year was as the result of a state-sponsored judicial killing.

Morsi was placed in solitary confinement for 23 hours a day, the experts explained. While in jail, "he was not allowed to see other prisoners, even during the one hour a day he was permitted to exercise."

"Dr. Morsi was held in conditions that can only be described as brutal, particularly during his five-year detentions in the Tora prison complex,", Agnes Callamard, Special Rapporteur on extrajudicial killings, together with the UN Working Group on Arbitrary Detention said Friday.

"Dr. Morsi's death after enduring those conditions could amount to a State-sanctioned arbitrary killing," they said in a statement.

"He was forced to sleep on a concrete floor with only one or two blankets for protection. He was not allowed access to books, journals, writing materials or a radio," the independent rights experts detailed in an "official communication" to the Egyptian government.

The experts say thousands of other detainees may be at "severe risk," many of them members of the Muslim Brotherhood, Mr Morsi's political party which was branded a "terrorist organization" by the coup leaders within months of them getting rid of the elected president.

Mr. Morsi, "was denied life-saving and ongoing care for his diabetes and high blood pressure" while incarcerated, the group went on, and consequently, "he progressively lost the vision in his left eye, had recurrent diabetic comas and fainted repeatedly. From this, he suffered significant tooth decay and gum infections."

Despite repeated warnings to authorities that such conditions would gradually undermine Mr. Morsi's health, to the point of killing him, "there is no evidence they acted to address these concerns, even though the consequences were foreseeable."

Prisoners 'effectively being killed by the conditions'

Former affairs adviser to the late President, Dr. Essam El-Haddad, and his son, Mr. Gehad El-Haddad, who was chief spokesman for the Muslim Brotherhood organization, are among the thousands of other prisoners enduring similar conditions.

"These two men are effectively being killed by the conditions under which they are held and the denial of medical treatment. It appears that this is intentional or at the very least allowed to happen through the reckless disregard for their life and fate," the experts noted.

"Thousands of other prisoners in Egypt may also be at risk of death or irreparable damage to their health because of inadequate conditions of detention, compounded by rampant violations of due process, including detention without charge, incommunicado detention, inadequate access to lawyers, and other practices preventing a fair trial."

"We have received reports of overcrowding, inadequate food, poor ventilation and no access to sunlight. Prisoners are denied family visits and fail to receive necessary medical care. Many are placed in solitary confinement for extended periods of time," the UN experts said.

The panel has called for an effective independent and impartial investigation into the unlawful death of Dr. Morsi and of all other prisoners who have died in custody since 2012, for the prosecution of the alleged perpetrators, and compensation for the victims' families. The methodology and results of the investigation should be made public, they said.

They urged Egypt to "reverse what appears to be deeply entrenched practices" on people's right to a life free of torture, ill-treatment, and the right to due process and medical attention.

These violations place Egypt's inmates at risk of death or "irreparable damage to their health", thus, the experts called for an effective and impartial investigation into Mr. Morsi's "unlawful deathand all other prisoners who died in custody since 2012."

The experts said they have engaged with the Egyptian government and will continue to monitor the situation and have offered their assistance to collaborate with relevant stakeholders to address the larger problem of dire prison conditions in the country.

The UN's High Commissioner for Human Rights, Michelle Bachelet, has previously expressed extreme concern for the country's prosecution approach, after the Egyptian court confirmed it would sentence seventy five people to death, and 47 to life in prison in a crackdown on Muslim Brotherhood-led protests in 2013. She called the sentences a "gross and irreversible miscarriage of justice."