GEOFF BENNETT: Syrians are celebrating their hard-won freedoms throughout the nation, but that joy is tempered by the absence of so many imprisoned and never heard from again, disappeared in the night and murdered in foreboding torture chambers.

In some ways, Syria is a land of ghosts, and the job of speaking for the dead now falls to their loved ones and to the new Syrian government.

Our Leila Molana-Allen reports now from the suburbs of Damascus.

A warning: Some of the images in this story are disturbing.

LEILA MOLANA-ALLEN: Bringing up the bodies.

As the full scale of the Assad regime's crimes against its people is discovered, Syrians are beginning to look for their loved ones underground.

This morning, they have opened a suspected secret burial site on a construction lot outside Damascus near one of the regime's most feared prisons, inside, bags filled with bones and human skulls.

AMMAR SALAME, Syrian Civil Defense Volunteer: We found seven bags.

The seven bags were numbered code names of prisoner, prisoner number blank, prisoner number blank.

LEILA MOLANA-ALLEN: So each of the bags was labeled with the number of a prisoner?

AMMAR SALAME: According to what we found, yes.

LEILA MOLANA-ALLEN: But no names?

AMMAR SALAME: The brand of the bag, it was a flour from Argentina, for example.

LEILA MOLANA-ALLEN: They were burying human bodies inside flour bags?

AMMAR SALAME: Yes, exactly, yes.

LEILA MOLANA-ALLEN: Syria's civil defense volunteers, the White Helmets, famous for pulling survivors out of the rubble of Assad's bombardment of the rebel-held northwest, are now working across the country to help secure grave sites.

What do you think has happened to these bodies when you discover them?

What condition are they in?

What has been done to them?

AMMAR SALAME: I think they were prisoners.

They died in the prison.

And they brought them here.

Some of the bones was broken.

LEILA MOLANA-ALLEN: And so the fact that the bones are broken, what do you think that means?

AMMAR SALAME: Of course, torture.

Torture.

LEILA MOLANA-ALLEN: Torture.

AMMAR SALAME: We need to search as Syrians to know what happened to our loved ones.

LEILA MOLANA-ALLEN: Across the country, mass graves like these are now being discovered.

Many Syrians long suspected where they were, but they weren't free to ask or look.

The priority now is to securely exhume these remains, so they can be identified and laid to rest, but also to gather vital evidence to prosecute those who committed these atrocities.

With more than 100,000 Syrians still missing, Ammar fears much of his country is now a graveyard.

AMMAR SALAME: This is also grave.

This is also a grave.

Look.

Look.

Yesterday, I received a call from a woman, a mother.

She lost her son 12 years ago.

He was arrested 12 years ago.

And she asked me about Sednaya, because there was a rumor there was people inside Sednaya crying under the ground.

I told her, no one.

It's empty.

Everyone was liberated.

And she said: "I wish, I hope Sednaya wasn't liberated, wasn't taken, because I still had hope before to have my son alive.

But now I am sure 99 percent is that my son is dead."

LEILA MOLANA-ALLEN: Now that the prison has been freed, she knows he's not there.

AMMAR SALAME: Yes.

LEILA MOLANA-ALLEN: And so she thinks she's looking for a body.

AMMAR SALAME: Yes.

Yes.

LEILA MOLANA-ALLEN: Finding dead ends searching prisons and hospitals, desperate families are now appealing to the public.

This monument in Central Damascus is covered in hundreds of posters of missing men, fathers, husbands, sons.

They contain the date when they were last seen before they disappeared and a phone number if anyone has any information.

As we read the posters, people approach us with the stories of disappeared loved ones begging for help.

Hanneh is walking the streets of Damascus clutching a fistful of pictures of her son Hassan.

I ask her what happened to him.

HANNEH QASSAR, Mother (through translator): In 2012, he went out with his cousin to buy bread.

He disappeared.

I don't know what happened.

But when they published the list of names at Sednaya prison, his was there.

LEILA MOLANA-ALLEN: Has she been able to find any information at all?

"No, nothing."

HANNEH QASSAR (through translator): Without him, there's nothing left.

I'm all alone.

LEILA MOLANA-ALLEN: As the country celebrates its newfound freedom after more than half-a-century of autocratic rule, every hope for the future is shadowed by the losses of the past.

And for those still searching, the agony of not knowing is making it impossible to move forward.

In the wrecked Damascus suburbs of Eastern Ghouta, a solitary mourner crouches over an unmarked grave.

MAHA GHAZI, Survivor (through translator): I want to know where my sister is.

What am I supposed to tell my mother now?

What should I tell her?

Let's enjoy the victory?

Where's the victory?

LEILA MOLANA-ALLEN: Maha is searching for her sister.

She was buried a decade ago, one of the thousands killed by Assad's chemical weapons stockpile.

She's no idea where, so she's chosen to mourn at this spot.

Until now, it's been forbidden to search or even speak of it.

MAHA GHAZI (through translator): We couldn't say a word.

No one inside the country could ever mention the chemicals.

We were so oppressed, we couldn't even cry or get treatment.

She was just 21 years old.

She was pregnant when she died.

And all my other siblings are spread across different graveyards.

LEILA MOLANA-ALLEN: In August 2013, regime forces launched rockets containing the chemical agent sarin on two rebel-held neighborhoods in the Damascus suburbs of Eastern Ghouta.

It was the deadliest chemical weapons attack since the Iran-Iraq War.

Barack Obama had warned the regime that using chemical weapons against civilians would force America's hand.

U.N. inspectors who searched the site confirmed significant quantities of the gas has been used in an indiscriminate attack.

In spite of international outrage, nothing was done to stop it happening again.

With her six siblings dead, only Maha and her mother are left.

Suffering the long-term effects of sarin without access to treatment, Maha's mother is blind and unable to walk.

Maha struggles to see well and has lost her sense of smell.

MAHA GHAZI (through translator): I got affected by the chemicals and suffered a lot because I stayed here.

There's nothing left for us.

We're dead inside now.

We just want things to get better from now on for the young ones.

They don't deserve to live any more years of war.

LEILA MOLANA-ALLEN: We still don't know exactly how many people were killed here, partly because of the veil of silence enforced on victims by the regime and partly because whole families were exterminated with no one left to mourn them.

Some estimates are as high as nearly 2,000 people killed in one day.

ZUHAIR DABBAS, Survivor (through translator): What we saw on the bodies of children, women and men from the chemicals was unfathomable.

We saw the foam coming out of their mouths, noses and ears.

There was blood coming out too, and their bodies were blue as if they'd been badly beaten.

LEILA MOLANA-ALLEN: Zuhair remembers every face, every mother and child.

It was he who buried their bodies, laid five or six on top of each other in each hole, because there were so many.

ZUHAIR DABBAS (through translator): Yes, they were mass graves.

We put each body beside the other, covered them with sand and then did the same all over again.

People were bringing piles of bodies from everywhere.

It was indescribable.

We stayed there for three hours burying them.

LEILA MOLANA-ALLEN: Rescuing as many of his neighbors as he could, Zuhair was too late to save his own mother.

As he rushed to take her to hospital, he collapsed from the effect of the poison floating through the air.

ZUHAIR DABBAS (through translator): I found her taking her last breaths.

There was no one to help me carry her, and I was so exhausted.

I went outside and fell down.

I tried to get up again and walked for about 20 yards, and then I recited my own last rites.

LEILA MOLANA-ALLEN: When Zuhair regained consciousness, his mother was dead.

He lost 25 members of his own family in the attack.

Zuhair and Maha want revenge for decades of suffering.

But with Bashar al-Assad and his family safely in Moscow under Vladimir Putin's protection, they're unlikely to get it.

The most they can hope for is to finally seek treatment for their many illnesses and to mourn their loved ones in the open at last.

MAHA GHAZI: What kind of butcher is he,putting all these people underneath the ground like this?

What have they done to deserve this?

May God take revenge on him.

I wish for Bashar al-Assad not to die until he sees the agony of mothers, my mom's agony, who wakes up every day asking about her little girl.

LEILA MOLANA-ALLEN: An entire nation seeking answers, seeking justice, the man responsible out of reach.

For the "PBS News Hour," I'm Leila Molana-Allen in Eastern Ghouta, Damascus.