Davao, Philippines (CNN) Clarita Alia doesn't look like she has many tears left. Her eyes tell the story of a life filled with grief.

She is frail, depleted and seems much older than her 63 years.

Alia sleeps in an empty, rundown stall -- the remnants of her small vegetable stand -- in the southern Philippines city of Davao.

The air is putrid. Raw sewage flows in a nearby gutter. Rats scurry amidst piles of trash. Such is life in the slums.

Clarita Alia has lost four sons in their hometown of Davao, where President Duterte served as mayor for 22 years.

Alia wonders what life would be like today if her sons Richard, Christopher, Bobby, and Fernando were still alive.

"Richard was always bringing me flowers. Christopher would kiss me," she says. "I'm still longing for my children."

Alia's voice breaks. Tears stream down her cheeks. Then she sobs. It's the cry of a mother who has lost a child. Only, she has lost four.

Her weathered hands tremble as she clutches a plastic bag with a small notebook and a handful of photos of her sons -- the only pictures she has left.

Alia shows pictures of her sons at home in Davao City, on May 8, 2016.

She explains how they grew up dirt poor, like pretty much everyone in the slums of Davao. Drugs and crime plagued their neighborhood.

When former prosecutor -- now President -- Rodrigo Duterte was first elected mayor of his hometown in 1988, Davao was dubbed "the murder capital of the Philippines."

Crime was out of control. Residents were justifiably scared to walk the streets at night. The new mayor declared open season on criminals by encouraging police and vigilantes to use lethal force to rid them from the streets.

By the time Alia's sons came of age, Duterte's brutal war on crime was in full effect in Davao. Alia tried to steer her boys away from the gangsters that seemed to rule the backstreets and alleys of the slums. But the lure of easy money, combined with peer pressure, proved irresistible.

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"My son Richard, the eldest, was about 15. And he was in the gang. But I told him please get out of that because Duterte already warned on the TV that your sons and daughters who are really into something (crime) should get out of the city because they will be killed."

Richard was first to die, in 2001 according to Alia. She says Christopher was killed later that year, and in 2002, Bobby was stabbed to death—all of those cases remain unsolved.

Fernando was in hiding for nearly five years before being stabbed to death in 2007 -- all of those cases remain unsolved.

Police told Alia her sons were thugs, "serial thieves," unable to be rehabilitated.

But according to Alia, that's what police always say when they shoot and kill "society's garbage" -- a term Duterte has used to describe street thugs, dealers, and other targets of his drug war.

Photos: Philippines drug crackdown Police patrol a shanty community at night during curfew on June 8, 2016 in Manila. Hide Caption 1 of 9 Photos: Philippines drug crackdown Some 1,000 people whom authorities accused of being drug users and dealers take an oath before local authorities after turning themselves in in Tanauan, the Philippines, on July 18, 2016. Hide Caption 2 of 9 Photos: Philippines drug crackdown A man authorities accused of being a drug user is fingerprinted during the mass surrender of some 1,000 alleged drug users and pushers in the Philippine town of Tanauan, located about 37 miles (60 kilometers) south of Manila on July 18, 2016. Hide Caption 3 of 9 Photos: Philippines drug crackdown A social worker gives counseling to those who have turned themselves in for drug-related crimes in the Philippines on July 18, 2016. Hide Caption 4 of 9 Photos: Philippines drug crackdown A woman cradles her husband, next to a placard which reads "I'm a pusher," who was shot dead in Manila on July 23, 2016. Hide Caption 5 of 9 Photos: Philippines drug crackdown A Philippine police forensic investigator displays packets of drugs and a hand gun found inside a shanty where members of a suspected drug syndicate were killed after a shootout with police on July 3, 2016. Hide Caption 6 of 9 Photos: Philippines drug crackdown A suspected female member of a drug syndicate is presented by police in Manila on June 22, 2016. Hide Caption 7 of 9 Photos: Philippines drug crackdown A gun, bullets, marked money and sachets of crystal meth are laid on a table after a drug raid in Manila on June 20, 2016. Hide Caption 8 of 9 Photos: Philippines drug crackdown Police officers stand in formation before the start of "Oplan Rody" on June 1, 2016, a law enforcement operation named after President Duterte, whose nickname is Rody. Hide Caption 9 of 9

Alia says death has become common in the city.

"That's the problem with our government here in Davao. People will do nothing even if they see somebody is being shot. They just don't care," Alia says.

During our interview, passing teenagers heckle Alia for openly criticizing Duterte, whose nationwide approval ratings are around 80%.

"People should speak up, especially the victims," Alia says. "If they remain silent, the suffering will continue."

She's one of the few in Davao who seems willing to say the killings must stop.

Duterte served seven terms as Davao mayor, leading the southern city for 22 years. Locals say he transformed Davao from one of the most dangerous cities in the Philippines to one of the safest, even though between 2010 to 2015, Davao City had the fourth highest number of crimes countrywide

The city hall in Davao, taken in early 2017, currently painted in Duterte's colors of white and brown which some locals say is "regal."

Duterte is the first Philippine president from the island of Mindanao where Davao is located, a point of immense local pride.

Even though the city's murder rate remains high, and despite the persistent terror threat in Mindanao , locals proudly claim they no longer live in fear.

They often speak of Duterte's father-like presence. Many describe him as a disciplinarian. That discipline includes strict rules. A nightly curfew for minors , a smoking ban, and an early cut-off for liquor sales.

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"He treats everyone as if they are part of a big family. If you did something wrong, then definitely you will be disciplined. If you did something bad you will be punished," says one woman at the night market.

"He's done a lot for the city in terms of keeping peace and order and inspiring people to be better citizens. He's a hands-on leader," another man says.

But Duterte is most revered for his crackdown on crime. He has admitted to personally shooting three people he calls criminals during his early days as mayor, though he later said he was among a group firing weapons and claimed he had no way of knowing if his bullets were the ones who struck their targets.

In any event, he has long encouraged police, and the public, to take matters into their own hands

A United Nations report and human rights groups documented a wave of hundreds of mostly vigilante killings committed by death squads across Davao during Duterte's long run as mayor.

Duterte has denied any involvement.

Duterte critic Father Amado Picardal at the Redemptorist Church in Baclaran, Philippines.

One of Duterte's most vocal opponents in Davao is Father Amado Picardal , a Catholic priest who has been assigned there for 16 years.

He runs a human rights group that claims to have tracked more than 1,400 murders in Davao over the last 20 years.

"This is wrong. We have to put a stop to this. Because if this continues it will destroy us as a country, as a nation," Picardal says.

"It is bringing out the worst in a lot of people ... Most of (those killed) will be poor, most of them will be users, and the problems of poverty will still be there. It is not addressed. It is going to bring us to ruin."