Sam Attar reckons he left part of his soul in Gaza. It was the part of him that saw suffering and could not turn away. The part which now cannot forget.

You can be on the shores of Lake Michigan on an overcast spring day, the wind whipping up waves on the green water. And at the very same time you can be back there, in the heat and the dying.

It's been three weeks since he came home to Chicago but it might as well have been yesterday. The faces of that other world are with him: Jenna, the traumatised little girl wasting away, spectral pale on a hospital bed, while her mother shows Sam a phone video of the child's last birthday. Happy days before the disaster.

Warning: This article contains details and images some readers may find disturbing.

Another mother whose 10-year-old son had just died.

"The mom just told me with just a blank numb stare on her face that he had just died five minutes prior. The staff had been trying to cover up his body with blankets but she just refused to let them. She wanted to spend more time with him. She was grieving, she was sobbing, and stayed that way for about a good 20 minutes, she just didn't want to leave his side."

Then there was the man in his 50s, forgotten in a room, having had both legs amputated.

"He had lost his kids, his grandkids, his home," Sam recalls, "and he's alone in the corner of this dark hospital, maggots going out of his wounds and he was screaming: 'The worms are eating me alive please help me.' That was just one just one out of… I don't know, I just I stopped counting. But those are the people I still think of because they're still there."

Sam is a sensitive, thoughtful man in his 40s, the son of two doctors, who was born and raised in Chicago and who works as a surgeon at Northwestern hospital in the city. While in Gaza he kept video diaries and filmed his experiences.

For two weeks in March and April - on behalf of the NGO Palestinian American Bridge - he worked in Gaza hospitals that were desperately short of everything except badly-wounded patients. On the day he entered Gaza this time around he was immediately confronted with the hunger crisis.

"We were just swarmed by people banging on the cars, some people trying to jump on the cars. The drivers… they just got it. They don't stop because if they stopped then people jump on the cars. They're not trying to harm us. They're just begging for food. They're starving."

Sam recounts his experiences calmly, as you might expect of a man trained to put patients at ease. Every day there was the relentless pressure of carrying out triage, deciding who could be saved, who was beyond hope. Patients lying on hospital floors surrounded by blood and discarded bandages, the air filled with the cries of pain and of grieving relatives.

There is no erasing such horrors. Even if you are a highly trained doctor with past experience of war zones like Ukraine, Syria and Iraq.

"I still think of all the patients I took care of," he says, "all the doctors that are still there. There's a little bit of guilt and shame at leaving because there's so much that needs to be done. The needs are overwhelming. And you walk away from people that are still there and still suffering."

The last trip - his third into Gaza since the war began - saw him join the first team of international medics to be embedded in a hospital in northern Gaza where malnutrition is at its most acute.

The mission was organised by the World Health Organisation (WHO) which has warned of looming famine. Some 30% of children below the age of two are reported to be acutely malnourished, and 70% of the population in northern Gaza is facing what the UN calls "catastrophic hunger."

Last month the UN Human Rights chief, Volker Turk, accused Israel of a potential war crime because of the food crisis in Gaza.

"The extent of Israel's continued restrictions on entry of aid into Gaza, together with the manner in which it continues to conduct hostilities, may amount to the use of starvation as a method of war," he said.

Israel denies this and has blamed the UN and aid agencies for any slow or inadequate delivery of aid.

The Israeli government said UN calculations on hunger were based on "multiple factual and methodological flaws, some of them serious." The government has said that it had tracked media reports that food markets in Gaza, including the north, had plentiful supplies.

"We outright reject any allegations according to which Israel is purposefully starving the civilian population in Gaza," said a statement from COGAT - Coordinator of Government Activities in the Territories.

Sam Attar remembers the 32-year-old woman admitted suffering from severe malnutrition, with her son, and her mother and father in the room with her.

She underwent CPR - attempts to resuscitate the heart - but could not be saved.

"I had to call it," Sam says. The young mother lay on a bench, her left arm dangling towards the floor, eyes gazing upward in the moment of death. Across the room a nurse comforted her crying mother.

There was the little girl, Jenna Ayyad, aged seven, "just skeleton and bone" whose mother hoped to get to the south where better medical facilities were available.

Jenna was traumatised by the war and looked to be extremely malnourished. She suffers from cystic fibrosis, which makes digestion more difficult. Her condition has been exacerbated by the conditions of the war and she is also suffering from trauma. In footage taken by a BBC cameraman Jenna seems lost and now only speaks to her mother.

"What can I do? She can't be treated," said Nisma Ayyad. "Her mental state is very difficult. She doesn't talk at all whenever anyone talks to her. Her situation is bad, and as a mom, I can't do anything."

Dr Attar said that as his team packed up to return to southern Gaza, Jenna's mother approached him.

"Jenna's mom came to me and was saying, 'I thought we were coming with you… what's happening? Why are you going and we're staying?"

Sam had to explain that the convoy south was only approved for the delivery of fuel and food and not for carrying patients.

But before leaving Sam and his colleagues filled in the necessary papers to have Jenna transferred. It would take days but they would make sure the paperwork reached the right offices. When Sam went to speak with Jenna's mother, other mums noticed.

"The problem is it's open, shared rooms, [with] maybe 10 patients in one room. So when all the other moms saw me talking to her, they all swarmed me."

Jenna was transferred and is now being treated at the International Medical Corps hospital near Rafah.

According to UN estimates last month the majority of those killed in the war have been women and children: 13,000 children, 9,000 women.

The war is now in its seventh month. Negotiations for a ceasefire and the release of hostages are stalled. Every day and night the wounded and the malnourished arrive at the few functioning hospitals that are left. The WHO says that only 10 of Gaza's 36 hospitals are still functioning.

Traveling in Gaza can be very dangerous for aid workers. Witness the deaths of seven aid workers, including three Britons, when the Israeli military attacked their convoy with missile strikes on 1 April.

Sam describes queuing for hours at Israeli checkpoints. "We often wait one to four hours depending on how long it takes for the Israelis to approve the passage because they are conducting military operations."

The US doctor wants to see a concerted push to get more aid into the north.

"The north just needs more access, it needs more food, more fuel, more water, the roads need to be opened… And there are so many patients that need to be evacuated from the north to the south and the problem is the south is also busy. I mean, the hospitals here are exploding."

He will go back. Soon he hopes. There are bonds of friendship which call out to him.

The paramedic Nabil who Sam saw every day, bringing in the wounded for treatment, until he himself became a victim who had to be pulled from the rubble by his colleagues. He is alive but will not be able to leave Gaza.

The doctor whose daughter was killed but who found the generosity to comfort a mother whose toddler son was suffering from a brain injury caused by bomb shrapnel.

And there are the patients and their families who see in the doctors, nurses and paramedics not just the possibility of practical help but the steady light of human decency in a place of terror and degradation.

These are Sam Attar's people. All of them.