.:-:. 'If He's Hiding, I Will Find Him.' One Man's Hunt for the Militants Who Killed His Father .:-:.

© Provided by The Wall Street Journal.

It was dark when Ahmad Sawadi buried his father, the body still clad in the bloodied robe shot through by militants only hours earlier.

Mr. Sawadi’s family and friends had risked their lives driving to the cemetery in eastern Syria. Artillery and gunfire between Islamic State fighters and Syria regime forces sounded dangerously close.

Standing at the fresh grave, Mr. Sawadi told the gathering he would abide by tribal tradition. “There will be no wake until the killer is killed,” he said. Mourning would have to wait for vengeance.

In the four years since burying his father, Mr. Sawadi has lost a brother, his village and his country. Chased into exile by Islamic State and kept from returning by Syrian government forces and U.S.-backed Kurdish forces, Mr. Sawadi, a burly 30-year-old, now lives in Istanbul, consumed with a mission.

Driven to seek justice and revenge, he works with dozens of fellow exiles and people still in Syria to track and publicize the whereabouts of Islamic State leaders on the run. A year ago, they set up the Euphrates Center Against Violence and Terrorism, a clearinghouse to distribute information for use by law enforcement or intelligence officials, mainly in Turkey and Europe.

Get news and analysis on politics, policy, national security and more, delivered right to your inbox

The group has posted 23 wanted posters of suspected militants with a photo, last known location and alleged crimes. Mr. Sawadi said 11 men have been caught by various authorities, a claim difficult to verify. The allegations are based on their years compiling an archive of videos, photos and witness statements about public executions, sex slavery, whippings and property theft.

Many Islamic State leaders have escaped the shrinking pockets of what was once a self-declared caliphate that stretched across swaths of Syria and Iraq. Some have fled with stolen fortunes, leaving behind mostly low-level fighters, said Col. Sean Ryan, spokesman for the U.S.-led coalition fighting Islamic State. They have been reported hiding as refugees among the same people they had once terrorized with their brutal interpretation of Islam.

Syria’s nearly eight-year war has left at least 400,000 people dead and millions more displaced. Yet there has been no comprehensive prosecution of war crimes or human-rights violations alleged against either Islamic State, the Syrian regime of President Bashar al-Assad or other parties in Syria’s multisided conflict.

In the absence of such justice, Mr. Sawadi and his team of amateur investigators are seeking their own—though they seem ambivalent at times whether the punishments need be court-imposed or extrajudicial.

One alleged militant was killed last year in northern Syria after the man’s wanted poster was shared on social media, according to Suhaib Jaber, a graphic designer for many of the group’s online posters. If escaping militants are killed by assailants, he said, “Why should we care?”

Other reprisal killings have been reported in Syria and the number could escalate. “In the absence of accountability and fair and impartial trials, it leaves the desire for retribution through legitimate channels unsatisfied,” said Balkees Jarrah, senior counsel for Human Rights Watch’s international justice program. “Tolerating impunity can contribute to renewed cycles of violence.”

Mr. Sawadi spends much of his time in an Istanbul restaurant mostly serving Syrian fare, often working through the night, fielding calls and text messages on his phone, which pings with every new tip.

Mr. Sawadi and his associates, most from Syria’s Deir Ezzour province, see each manhunt as personal. “They have all lost someone,” Mr. Sawadi said.

Among those in Mr. Sawadi’s sights have been two men—the one who fatally shot his father and, second, an Islamic State commander whose atrocities in Deir Ezzour he witnessed firsthand.

This year, he finally tracked one of them down.

Mr. Sawadi worked as a manager at the Four Seasons hotel in Damascus when Syria’s anti government protests began in March 2011. He joined other demonstrators, who called first for reform and then, after the regime’s brutal response to street protests, demanded the ouster of Mr. Assad.

Mr. Sawadi was arrested and detained for months. His father, a livestock dealer also working in Damascus, urged him to stay away from the uprising.

As the conflict deepened, Mr. Sawadi returned home to Deir Ezzour, where he, like others in Syria, began documenting the violence. He recorded and posted videos showing how civilians were killed in regime airstrikes on areas controlled by anti government rebels.

Islamic State emerged in Syria in 2013, taking advantage of the country’s growing chaos. Its militants tore through areas that had been under rebel control, including in eastern Syria. They soon took root in Deir Ezzour.

Mr. Sawadi urged his father to stay in Damascus, but in the spring of 2014 the elder Mr. Sawadi returned to Deir Ezzour to visit his aging mother.

During the father's visit, militants stormed the western side of the family’s ancestral village of Tabiyet. Most residents fled to the eastern half, but Mr. Sawadi’s grandmother was among those who refused to leave her home.

Late one night, believing the militants had withdrawn, Mr. Sawadi’s father went to check on the grandmother. His body and those of several relatives were found hours later on a dirt road. More than a dozen villagers were killed.

Mr. Sawadi began investigating his father’s death. A local shepherd told him he had seen the shooting and recognized three of the attackers from a neighboring village. The men shot from a rooftop at people in the street, Mr. Sawadi said the shepard told him; a fourth man waited in a vehicle.

Later, he heard the militants had boasted about the attack to others in their village, saying they had killed religious apostates.

Mr. Sawadi narrowed down the identity of the man he believes killed his father, based on a report of the gun carried by the shooter. He later got further confirmation when elders from the militants’ village visited Mr. Sawadi’s uncles and offered a blood debt for the father’s murder.

In tribal tradition, money is paid to the victim’s family to settle a killing. The uncles refused the payment, telling the elders to speak with Mr. Sawadi and his brothers. Mr. Sawadi said his family wasn’t interested in forgiveness.

Two months after his father’s death, in August 2014, one of Deir Ezzour’s largest tribes, al-Sheitat, clashed with Islamic State. In response, militants attacked oil fields controlled by the tribe, executing dozens of workers and shelling several villages, according to the United Nations Independent International Commission of Inquiry on the Syrian Arab Republic and human rights groups. An estimated 700 people, including women and children, were killed.

Witnesses later said an Islamic State commander named Kaser Haddawi took part in the shelling of villages and the execution of civilians. Mr. Haddawi had been one of the first local Syrians to join Islamic State, Mr. Sawadi said.

During the first few days of the Islamic State attack, Mr. Sawadi and others sneaked out at night to document the carnage, taking photos and videos. Many of the bodies had been beheaded or had slit throats.

“We held heads in our hands,” Mr. Sawadi said.

Soon after, he fled Syria to Turkey.

Justice for victims of Syria’s war remains largely out of reach. Some two dozen court cases or investigations are under way in European countries.

Defendants include the Syrian regime, Islamic State members and former antigovernment rebels. The cases have yielded only a handful of convictions of low-level perpetrators—none for those who ordered the war crimes. These national courts, however, face questions over legal jurisdiction as well as the difficulty of collecting evidence from a distant war zone.

Islamic State militants captured in Syria are held mostly by U.S.-backed Kurds, who have only a limited ability to prosecute them.

“An ideal scenario would be a framework combining international and regional and national courts, each taking a part of the accountability process. That is not what we have at the moment,” said Catherine Marchi-Uhel, a former French judge. She heads the U.N. International, Impartial and Independent Mechanism, a panel created in 2016 to investigate and prepare cases for the most serious crimes in the Syrian conflict.

Given the sheer number of crimes, she said, many won’t be prosecuted.

After the death of Mr. Sawadi’s father, the rest of his immediate family migrated to Europe—all but Mr. Sawadi’s youngest brother, Ali, who instead returned to Syria to avenge his father his own way. The 18-year-old joined rebels fighting Islamic State. Late last year, he was killed in battle.

“I know he went because of baba,” Mr. Sawadi said.

In January, Mr. Sawadi was about to board a plane when he got a message from a source deep in Islamic State territory: Mr. Haddawi, the Islamic State commander who participated in the shelling of civilians in Deir Ezzour, had slipped out of a militant-controlled village.

That night, a photo of Mr. Haddawi—who had risen to become a lieutenant of Islamic State leader Abu Bakr Baghdadi—was on a wanted poster from the Euphrates Center, captioned “War Criminal.”

Mr. Haddawi had paid smugglers to ferry him on back roads in Syria’s desert to elude the checkpoints of U.S.-backed armed forces, the source said. In March, Mr. Sawadi learned Mr. Haddawi was in Gaziantep, Turkey.

Within hours, he updated Mr. Haddawi’s location on the wanted poster.

Turkish intelligence agents who monitor the Euphrates Center site saw the Islamic State commander was in Gaziantep, a Turkish official said, but authorities there couldn’t locate him.

Mr. Haddawi surfaced a month later in Izmir, Turkey, once a busy hub for migrants and refugees seeking illegal passage to Europe. Mr. Sawadi debated whether to update the wanted poster, fearing the militant would be tipped off.

Separately, Turkey’s intelligence agency heard about a desperate man in Izmir, possibly a fleeing militant, who offered large sums for boat passage to Greece. The agency has a network of informants, including smugglers and refugees, to help stem terrorist attacks, Turkish officials said.

On April 19, Turkish intelligence and antiterror police raided the home of a smuggler and took Mr. Haddawi into custody.

Weeks after Mr. Haddawi’s arrest, Mr. Sawadi began receiving threats from an anonymous Telegram account. “Revenge is close and the active volcano is ready to burn you,” one message said. His Telegram account was later hacked, Mr. Sawadi said, exposing his many contacts.

Mr. Sawadi’s wife sometimes asks her husband to quit. Mr. Sawadi’s mother, who lives in Germany with six of his siblings, urges Mr. Sawadi to join them. “She already lost a husband and one son,” he said. “She doesn’t want to lose another.”

In the past year, Mr. Sawadi has heard of several belated wakes for victims of Islamic State, held after their assailants were confirmed dead. He is waiting to do the same for his father, he said, hoping family members still in Syria will carry out the vendetta.

“If I was in Syria,” he said, “I would shoot him myself.”

At least two accomplices of his father’s killer are believed to have died in battles against U.S.-backed Kurdish fighters, Mr. Sawadi said.

With the U.S.-backed coalition now poised to capture the last remnants of Islamic State territory in eastern Syria, Mr. Sawadi worries the military could derail the family’s vengeance.

Mr. Sawadi believes the man who killed his father is in Hajin, one of the last towns controlled by the militants. Yet it has been months since he received word of a sighting.

“If he’s hiding, I will find him,” he said, “even after one year or after 10 years.”

Write to Raja Abdulrahim at: raja.abdulrahim@wsj.com