taken from a video of the horror that unfolded here last year: a procession of Shiite men, shot in the head one by one by Islamic State fighters and shoved into the waters of the Tigris.

“It’s just because we are Shia,” said Halil Kareem Garim, 61, standing near the river as he recalled the cousin he lost. “We don’t have any problems with Sunnis — we are praying to the same God. It is their mentality. They hate us.”

The riverbank has become a memorial of the massacre and a site of Shiite pilgrimage, already taking a prominent place in Iraq’s ledger of sectarian atrocities. In all, roughly 1,700 Shiite military personnel from the Camp Speicher base are believed to have been methodically gunned down by the Sunni extremists at Saddam Hussein’s old palace complex in Tikrit last June.

Now, five weeks after pro-government forces retook Tikrit from the militants, 11 mass graves are being unearthed, and the first few dozen sets of remains have been sent to Baghdad for identification and eventual release to the families.

Along with their grief, Iraqi Shiites are reckoning with the aftermath of a massacre that ranks as the worst since Mr. Hussein’s rule but also feels painfully familiar — another episode in what the Shiites view as a tragic history of oppression by the country’s Sunni minority.

“The Shia are always suffering,” said Muhammed Abdella, 24, a Shiite militiaman guarding the site by the river. He added, “We have been ruled by so many people, and the suffering continues.”

The killings, and the reactions to them, are stark reminders that meaningful sectarian reconciliation in Iraq has proved elusive and is likely to remain that way even if the Islamic State, also known as ISIS or ISIL, is defeated. Even though some Sunnis and Shiites have linked causes in fighting the militants, the weight of accumulated grievances seems to only grow.

The site by the Tigris has become a shrine of growing importance, with a plaque, flowers and passport-size photographs fastened to a railing by grieving families. There is a banner to honor the Shiites’ heroes: Grand Ayatollah Ali al-Sistani, the top Shiite cleric; Ayatollah Ali Khamenei, the supreme leader of Iran; and Qassim Suleimani, the Iranian spymaster and military leader whom the Shiites see these days as their most important patron. Relatives of the dead, mostly from the Shiite-dominated south, have been coming on trips organized by the government.

In Baghdad, relatives of the missing have been told to go to the morgue to give blood samples for DNA tests to compare with those of the bodies from the mass graves. The process is slow — slightly more than 200 bodies so far have been unearthed and brought to the morgue in Baghdad for testing — adding to the grief of families whose priority is proper burials for their loved ones.

“The whole project is in the first steps,” said Dr. Zaid Ali Youssef, the director of the Medical-Legal Unit at the Health Ministry, who is responsible for the morgue.

Mr. Garim, the man grieving recently at the riverbank, saw the massacre in the context of history. He ticked off his family’s losses in Iraq’s other traumas, which disproportionately affected the Shiites: He lost five relatives in 1991 when a Shiite uprising was brutally put down by Mr. Hussein; seven relatives were killed in the bloody war against Iran in the 1980s; and in more recent times, he lost family members in sectarian attacks and car bombings.

His story is not uncommon. Across the Shiite south of Iraq, it seems in every house there is a story of tragedy.

Recently, a group of families gathered at Hassan Shimran Alwan’s house in Hamza, in southern Iraq; all of them had sons missing from Camp Speicher. They viewed the killings in June as the continuation of generations of slaughter and sacrifice for their fellow Shiites.

On the walls were symbols of Shiite power in the face of oppression: antique guns Mr. Alwan said were used in the 1921 uprising against the British, pictures of family members who resisted Mr. Hussein’s regime, and a photograph of the Shiite cleric Moktada al-Sadr.

That the Islamic State leadership counts several former officers in Mr. Hussein’s regime, not to mention that the massacre took place on the former dictator’s palace grounds, has reinforced a sense among the Shiites that their suffering under the Baathists has never ceased.

“This crime specifically happened because of the old regime,” Mr. Alwan said, adding: “We want a fair government that gives the best of the services to the people and doesn’t distinguish among the sects. Shiites are peaceful, deprived people.”

That view is not shared by Sunni Arab Iraqis who have suffered abuse or say they have lost family members to summary killings by Shiite militiamen after the groups seized territory back from the Sunni militants. In the light of such reports, the Shiite-led military and militia offensive to retake Tikrit, in the heart of Sunni territory, was watched with more than a little trepidation since its start in March.

But the aftermath of that offensive is now seen by some as a sign that the dynamics of Iraq’s sectarian violence have been shifting, if not disappearing.

In 2006, when Sunni extremists from Al Qaeda in Iraq — the predecessor to the Islamic State — blew up the dome of an important mosque in Samarra, the attack set off tit-for-tat sectarian bloodletting that nearly tore the country apart.

Now, many of the same Shiite militias that took part in that mayhem have become more professionalized and led the fight against the Islamic State in Tikrit. Though there have been reports of looting in the city and, in one publicized case, a lynching of a suspected Islamic State fighter, by most accounts the Shiite forces have remained largely restrained.

For some Shiite families who have been awaiting word since June about sons and brothers among those missing from Camp Speicher, the discovery of the mass graves in Tikrit intensified sad vigils.

On a recent afternoon in the Sadr City district of Baghdad, three brothers, who lost their father in a shooting in 2005 that they attributed to sectarian violence, sat on the floor in their family’s reception room and spoke of a brother who had been posted at Camp Speicher. They were not yet willing to concede his death, and they said they had hope he was still alive.

If he is not, though, “we most care about his body,” said one of the brothers, Dhia Najim, 37. “We want to show it to our mom.”

At an orphanage in Baghdad, a young Shiite boy has turned his anguish into art. An accomplished painter at 14, Hussein Alaa, who lost both parents in a car bombing several years ago, saw the gruesome video of the Speicher killings on television. The only thing he could do was sit down and paint. The result was a haunting picture of men, kneeling and handcuffed, with the faces of wailing mothers in the background.

“I felt very sad,” he said, “and thought, ‘Why did this happen to these people?’ ”