Israel's National Center for Forensic Medicine has tested skeletal remains for decades.

For decades, Israel's National Center for Forensic Medicine has tested skeletal remains secreted across its northern border, checking whether the DNA matched that of Israeli soldiers missing in action behind enemy lines in Lebanon or Syria.

"From time to time they'd bring the samples," said Chen Kugel, the head of the forensics center. "It's body remains. It's bones. It was always: maybe this time, maybe this time, maybe this time."

There was never a match.

Then, earlier this year, a bag of bones arrived, and from the moment it was opened, it looked promising. The staff soon determined that the bones belonged to Staff Sgt. Zachary Baumel, who had gone missing in Lebanon 37 years ago.

Baumel's body had been recovered from a cemetery in a Palestinian refugee camp on the outskirts of the Syrian capital Damascus, still enemy territory since Israel and Syria remain in a state of war.

Israel's National Center for Forensic Medicine received a bag of bones this year. They were found to belong to the soldier.

Residents of the camp had grown up hearing rumors that the bodies of missing Israeli soldiers were hidden among the tombstones, but the exact whereabouts of their remains were a closely held secret.

Digging began in the cemetery as early as 2013, residents said in interviews, and over the years rebel groups and Islamic State militants all raced to find what would be a highly prized bargaining chip in the context of Syria's chaotic civil war. Israeli officials long watched the shifting dynamics of that war, waiting for a moment when they might be able to retrieve any of their fallen soldiers.

Eventually, Russian troops, which had intervened in the war to support Syrian President Bashar al-Assad, obtained Baumel's body, and they returned it to Israel.

But the search is not finished. Syrian opposition activists said in interviews that Russian and Syrian soldiers are continuing to dig in the cemetery, hunting for the bodies of two other Israeli soldiers who went missing alongside Baumel. However, an official close to the regime said the soldiers were protecting the graveyard, rather than excavating it. The Russian embassy in Tel Aviv declined to comment.

Israeli and Syrian forces clashed in June 1982 during the Battle of Sultan Yacoub in Lebanon's Bekaa Valley, and Israeli troops had invaded Lebanon just days earlier, targeting the presence of the Palestine Liberation Organization.

Baumel, an American Israeli born in Brooklyn, was driving a tank when his unit was attacked by Syrian forces. The tank was struck, and Baumel and his crew leaped from the burning vehicle, only to come under fire.

Baumel was later declared missing, along with five comrades.

"From time to time they'd bring the samples," said Chen Kugel, the head of the forensics center.

Dean Brelis, a reporter for Time, later said he had seen several Israeli soldiers paraded through Damascus along with their captured tank. They came to stop outside the headquarters of the Defense Brigade Commandos, an elite force headed by Rifaat al-Assad, the brother of Syria's president at the time. Images taken of the parade, however, were too grainy for a positive identification of any Israelis.

One of the crew, Staff Sgt. Ariel Lieberman, who was captured by Syrian forces a day after the battle, was released in a prisoner exchange two years later. In 1985, two Israeli captives from the war, including Baumel's tank commander Hezi Shai, were released in another exchange with the Popular Front for the Liberation of Palestine - General Command, a Palestinian militant group close to the Syrian government. The body of another tank commander in the unit was also eventually turned over.

Even Baumel's tank was ultimately returned. It had been handed over by the Syrians to Russia, which had put it on display at the Moscow Tank Museum before Russian President Vladimir Putin granted the request of Israeli Prime Minister Benjamin Netanyahu and returned it in 2016.

But there was no sign of Baumel and his comrades cannon loader Zvi Feldman and Cpl. Yehuda Katz.

Palestinians living in the Yarmouk refugee camp, where tents had long been replaced by tightly packed cinder-block buildings, might have dismissed the rumors of buried Israeli bodies as just that. But about a decade ago, the residents started receiving anonymous calls and text messages, widely believed to be from Israeli intelligence, offering rewards for information about the corpses. Camp residents grew convinced the bodies were in the cemetery somewhere.

Everyone knew it, everyone," said Thaer al-Sahli, a poet and filmmaker who fled Yarmouk for the Netherlands in 2014.

Forensic experts are checking whether the DNA matched that of Israeli soldiers missing in action behind enemy lines in Lebanon or Syria.

But where exactly the bodies were buried was a secret closely held by senior members of the Palestinian militant factions in charge of the camp, the PFLP-GC and Fatah.

As Syria slid into civil war in 2011, control of the camp shifted to Syrian rebels and Palestinian groups fighting against Assad's government.

Although Netanyahu has said he put in a request to Russia to retrieve the bodies in 2017, Yarmouk residents say Israel had turned to Syrian rebel groups for help much earlier than that, the residents said.

In 2013, one rebel group dug a hole near the entrance to the cemetery, three residents recalled. The rebels claimed to be searching for old weapons hidden in the 1980s, but not all were convinced. Then, when Islamic State militants stormed the Yarmouk camp in 2015, they were no doubt aware that the graveyard contained a valuable prize.

"They were digging between the tombstones for quite a while," said one resident, who spoke on the condition of anonymity for security reasons. Another resident said the militants used the excuse of smashing heathen tombstones to search the grounds.

Over the years, the Russian troop presence had been building, turning the tide of war against the Syrian rebels, and Israel sought out Moscow's help. During negotiations over the surrender and withdrawal of the rebels, the Russians in turn asked these opposition forces last year to help retrieve something from the cemetery, according to a person with knowledge of the talks.

"It was a race against time, a competition between ISIS, which was still looking for these corpses, and the Russians who also wanted to have these corpses," this person said. "That's why they demanded the support of the opposition to get in and get out."

Russia later revealed that it launched an operation into Islamic State territory around that time in an effort to retrieve Israeli bodies. The Russian ministry of defense said Israel had provided specific coordinates, but the operation did not succeed. The Russian troops came under attack, and a Russian special forces soldier was injured.

Finally, in an effort dubbed Operation Bittersweet Song by Israel, Baumel's body was successfully brought back. Israel and Russia have released few details about the mission nor disclosed how the remains were transferred to Israel. But an Israeli military official, who spoke on the condition of anonymity because the information has not been officially released, confirmed his body was retrieved from Yarmouk. Putin said it was pulled off with "Syrian partners."

The dilapidated appearance of the squat, three-story building set back from the road in Tel Aviv belies its central role in Israel's efforts to recover its war dead. It is the only forensic center in Israel.

The forensics center compared the remains with a database of DNA from relatives of those missing.

The center had previously obtained samples suspected to be from Guy Hever, a soldier who went missing after walking off his base in the Golan Heights in 1997, but they weren't. Nor was there a match for several other samples thought to belong to Ron Arad, a pilot who went missing in 1986 after ejecting from his airplane during a bombing mission over southern Lebanon.

When the bags from Yarmouk finally arrived, they were opened in a basement room. "One of the bodies was very dramatic," recalled Kugel. "After cleaning of course, we saw the soles of the shoes with printing in Hebrew. We saw the military overalls, with Hebrew at the back, so we understood it might be someone that we were looking for."

The forensics center compared the remains with a database of DNA from relatives of those missing and found a match. When the confirmation came, some of the officers accompanying the body cried, Kugel said. "In Israeli culture it's very important to show that we look after the soldiers and bring them home," he said.

The forensics center would not disclose how and when Baumel died. But Haim Cohen, a forensic anthropologist, said there was no sign of him being shot. He suffered blunt force trauma to the pelvis and the hand. The injury to the hand was around the time of death, he said.

A green residue on the bones indicated he had been buried in a metal coffin.

Baumel was finally laid to rest in a military funeral in Jerusalem in April.

Palestinians in the Yarmouk camp have traded accusations over who betrayed the location of Baumel's body to the Russians.

The Fatah party, which had a historic role overseeing the cemetery, has denied revealing the information. Anwar Raja, the senior commander in Yarmouk of the rival PFLP-GC group, also said it was not involved in the retrieval of the bodies.

"The Russians themselves got in and got them out," Raja said. He added that the Russians had taken away about 10 bodies.

Israel said it did not make a deal in exchange for the bodies but in a gesture of goodwill released two Syrian prisoners.

At the forensics center in Tel Aviv, the staff examined all the remains that were provided but without making any other matches. Most of the Syrian bones were taken away by the Israeli military, according to the staff, though one remained on a recent day.

"From Syria, not Baumel," explained Nurit Bubil, picking up a large thigh bone from the counter of her DNA testing laboratory. The military would soon come and collect it, she said.

Lt. Gen. Jonathan Conricus, a spokesman for the Israeli military, said the unidentified bodies were likely to be Palestinian and would be buried in a "terrorist graveyard" of unmarked graves in an undisclosed location.

For Palestinian refugees from Yarmouk, the excavation of their cemetery, now pillaged and badly damaged, is the latest in a long series of painful episodes. They have called on Israel to return those remains that do not match missing Israelis.

"It is a matter of dignity for us, Yarmouk graveyard. Our leaders are there, our sons," said al-Sahli. "They took these bodies with no respect. These bodies should remain with their families, just like those of Baumel and the other soldiers."