Palestinian surgeon Khaled Al Serr was working at Nasser Hospital in Khan Younis in southern Gaza on March 25 when he was arrested and detained in a raid by Israeli troops.

For months, his family had no knowledge of his whereabouts until other detained health-care workers were released and informed Al Serr's loved ones about where he was.

After spending more than six months in Israeli custody, the 32-year-old doctor was released on Sept. 29 from Ofer military prison in the occupied West Bank, without any charges or trial.

"It was like a nightmare," Al Serr told CBC News of his detainment, two days after he was released and let back into Gaza.

While in custody, the doctor alleges, he was tortured, humiliated and denied adequate access to medical care by soldiers and prison guards. 

"I was lucky that I [came] back to my family with a complete body ... [that] I did not lose my feet," he said. "Some of the prisoners there had an infection due to the dogs there that bit their leg — and some of them due to the health-care negligence there." 

He said when Israeli forces raided the hospital, staff had been trying to clean and reorganize it so they could reopen to patients. The facility closed in February following an earlier raid that devastated much of the upper floor and stripped it of supplies.  

145 doctors still in Israeli custody: Gaza Health Ministry

Al Serr's experience is one that hundreds of health-care workers in Gaza have undergone. Roughly 300 health-care workers from Gaza remain in custody after being arbitrarily detained by Israeli forces while on duty, according to the local Health Ministry. At least 145 of them are doctors — roughly seven per cent of the estimated 2,110 physicians remaining in Gaza. The raids on health care facilities and detainment of medical staff are devastating to an already fragile health-care system, international rights organizations say.

Since June, Amnesty International had repeatedly called on Israeli forces to release Al Serr, pointing out that his fate and whereabouts remained largely unknown to his family until July. 

The global human rights group says Al Serr was detained along with other medical staff in the Nasser Hospital raid and called on the military to disclose the whereabouts of all Palestinian health workers who it says were "forcibly disappeared."

WATCH | What 6 months in Israeli custody looked like for this doctor:

Gaza doctor released after being detained in Israeli custody for more than six months

Dr. Khaled Al Serr was released by Israeli forces on Sept. 29 after spending more than six months in Israeli prisons. The 32-year-old surgeon, who works at Nasser Hospital in Khan Younis in Gaza, said he was interrogated, humiliated and beaten only to be suddenly released last week without any charges.

The Israel Defence Forces (IDF) acknowledged it has arrested medical staff in the course of its military operations in Gaza, but did not say exactly how many or give details of Al Serr's detention.

"In light of the extensive exploitation of medical facilities [by Hamas], individuals in Gaza, including medical teams, have been apprehended and questioned based on intelligence indicating their involvement in terrorist activities," it said in a statement to CBC News. Hamas has denied such allegations.

"Those found to have no involvement are released after questioning," the IDF added.

It said that in its raid of Nasser Hospital in February it found weapons as well as medicines with the names and photos of Israeli hostages on them. It said it has apprehended "hundreds of terrorists and other terror suspects who were hiding in the hospital, some of whom had posed as medical staff."

The IDF has also aired footage taken by its troops that it says showed tunnels containing weapons below some of the hospitals it has raided.

"Regrettably, Hamas continues to put Gaza's most vulnerable citizens in serious danger by cynically using hospitals for terror," it said.

Asked by CBC News if the IDF can confirm 300 health-care workers were in Israeli custody, the military did not say.

Punishment, humiliation in Israeli custody: Al Serr

For the first five days in custody, Al Serr said. he was interrogated about his work inside the hospital, why he was living at the hospital and his whereabouts on Oct. 7, 2023, during the Hamas-led attacks on Israel that left 1,200 people dead. 

He said before being taken to a prison, he was put in a shipping container with roughly 100 other prisoners, where he was beaten and left without any medical services. Al Serr said he was not allowed to be treated even though he was having difficulty breathing and coughing up blood.

He developed a skin rash, with pus-filled bumps and redness covering his arms.

"They left us to suffer from any disease," he said. "This is part of the punishment inside the prison."

Then, he said he was transferred to Sde Teiman, an Israeli military base in the Negev desert now used as a detention camp, where he says he was forced to sit down with his hands shackled and not allowed to move, speak or look at anyone. He says he was blindfolded and handcuffed for 24 hours in the day and he was allegedly mocked and sworn at by soldiers.

WATCH | Another ex-detainee details forms of punishment at military base-turned jail:

Man pictured in viral photo at Israeli prison speaks

Ibrahim Salem's photo at the Sde Teiman prison in Israel's Negev desert went viral after it was leaked to CNN and spread on social media. Salem says standing at the fence with his arms up as he was seen doing in the photo, was a form of punishment he endured during his 52 day detention in the military base turned jail.

He said he was there for roughly 80 days without knowing why he was being held before he was taken to Ofer prison, not knowing what day or month it was.

"I have suffered a lot of punishment and beating from the soldiers there without any charge," Al Serr said.

"As a doctor, I did not have special treatment because all of the people there, or most of them, were … professors and … teachers, doctors, nurses. Everybody there has an equal treatment, which is punishment and humiliation from the Israeli soldiers."

Family didn't know if Al Serr was alive

Meanwhile, for months, his fate and whereabouts were unknown to his family. 

His father, Abdul Karim Al Serr, who was in Rafah at the time of his son's detainment, said he initially thought he lost his son in an airstrike. But after family members could not find him among those killed, they determined he was missing. 

The elder Al Serr didn't know about the raid until a nurse, who had been arrested alongside the doctor, told him that his son was in Israeli custody and was alive. After that, the elder Al Serr said, he would ask every person released from Israeli prisons about his son, hoping to get information on his well-being. 

"We would check in on him. Between the sadness, between the pain and the suffering, the [other detainees] would tell us what they endured in prison," he said.

When his son was released after six months in custody, Al Serr said he had no idea. He said he was in Khan Younis, outside of a makeshift home atop rubble, when his son walked up to him, but the father did not recognize him.

"I was surprised. I looked at him. Who's that? That's not Khaled," he said.

He said his son lost between 50 and 60 kilograms in prison and looked "half his size."

"I didn't think he would be released, even though he is a doctor. Everyone is supposed to respect him, to appreciate him — enemy or friend," his father said.

"Respect that he is a doctor. If a Jewish [patient] comes to him, he would treat him. If a Christian comes to him, he would treat him. If a Muslim comes to him, he would treat him."

Workers' arrests strain a fragile health-care system

Amnesty International said detainees, including the younger Al Serr, have been held with no means of communication, "outside the protection of the law, in conditions amounting to enforced disappearance" that violate international human rights law.

Amnesty has cited Israel's unlawful combatants law, which grants the country power to detain anyone in Gaza that it suspects of engaging in hostilities against it or posing a threat to security. It alleged that Israel uses this law to "arbitrarily" detain Palestinian civilians without due process, calling for it to be repealed and those detained under it released.

"Since Oct. 7, 2023, and particularly since the start of ground operations in Gaza at the end of October, Israeli authorities have used the [law] to detain thousands of Palestinians without charges or trial," Amnesty International wrote on its website in June.

Since the onset of the Israel-Hamas war, a total of 595 health-care workers have been killed in Gaza and the West Bank by Israeli forces as of Sept. 20, according to Healthcare Workers Watch.

The arrests of health-care workers are further straining Gaza's tenuous health-care system more than a year into a war that has devastated its infrastructure and injured at least 97,590 people and killed more than 42,000 in Israeli bombardment, according to Gaza health authorities.

Dr. Ahmed Al-Farra, head of pediatrics at Nasser Hospital, said hospitals in Gaza are in a "catastrophic situation."

Al-Farra said hospitals lack supplies, equipment and fuel to generate electricity, in addition to the unsanitary conditions and overcrowding they are dealing with.

Al-Farra said the lack of clean water and rampant spread of diseases are contributing to more and more deaths.