Jamil Hassan, one of the most feared men in Bashar al-Assad's Syrian regime, wanted for the torture and killing of civilians, was shaking as he walked down the stairs of his apartment block.

Outside, the 72-year-old climbed into a car in a small convoy with his family and a handful of security guards, just a few suitcases between them.

His neighbour and her teenage son watched.

"I knew the moment I saw them flee that Assad had fallen," she says.

When we entered Hassan's apartment a few days later, signs of the family's hasty departure were everywhere.

In the fridge was a half-eaten carrot cake with a knife still on the plate. The beds were strewn with clothes and empty shoeboxes. Flowers wilted in a vase in the dining room, and cups and plates had been left to dry by the sink.

A framed photo of a smiling Hassan and Assad hung on the wall of the study, with text reading: "Our skies are for us and forbidden to others".

Hassan, referred to as "the butcher" by many civilians on his street, was one of Assad's most menacing enforcers. He led the Air Force Intelligence and oversaw a network of detention facilities including the notorious Mezzeh Prison, where detainees were routinely tortured.

He is one of many senior regime figures wanted or sanctioned around the world who have abandoned their homes in affluent areas of Damascus and vanished.

Finding these men who ruled Syria with an iron fist will be difficult. Some fear they will strike political deals abroad and evade justice.

Hayat Tahrir al-Sham (HTS), which led the campaign to topple the regime, has vowed to search for them inside Syria. Rebels aligned with the group now occupy Hassan's apartment and a handwritten note on the front door warns people not to enter.

When we asked them where Hassan might have gone, one grinned and replied: "I don't know - to Hell."

Many apartment shutters on Hassan's quiet street in central Damascus are now closed. Knocks on doors go unanswered.

Those who will speak tell us about their fear at living on a street with a wanted war criminal. "We were so afraid to talk," says the woman who watched him flee. "It was terrifying to live next to them."

Hassan is wanted in the US for "engaging in conspiracy to commit cruel and inhuman treatment of civilian detainees, including US citizens". He was convicted in absentia earlier this year in France for his role in imprisoning, disappearing and torturing two Syrian-French nationals. Germany wants him too. An Interpol Red Notice shows a photograph of Hassan alongside a note that he is wanted for "conspiracy to commit war crimes".

He was placed under travel bans and had his assets frozen over the repression of civilian protesters. In April 2011 the US says Air Force Intelligence personnel fired tear gas and live ammunition at protesting crowds in Damascus and other cities, killing at least 43.

People on the street describe a formidable figure who was unapproachable and always surrounded by guards.

A makeshift security post outside Hassan's apartment building was constantly staffed by military personnel. The night before the regime collapsed, the men simply took off their uniforms and discarded their weapons, according to another neighbour.

"It was the first time I'd seen this post with no lights, no sounds, no noise," says 27-year-old Amr al-Bakri, a filmmaker who lives with his family in the building next door.

He said locals "knew what he did to the Syrians - outside of Damascus and in Damascus - so we know it but we can't say anything, just 'good morning sir'. He'd say nothing back."

Amr says his family had to give away their pet dog after Hassan's guards threatened to kill it if it didn't stop barking. When Amr's family asked for the guard post to be moved from outside their home, they were told they should move house instead, he says.

The guards would run regular inspections on the street and check the bags of visitors.

"Sometimes if I had a plumber or handyman to come and fix something one of the guards would come and check if there was really something that needed to be fixed," says the woman living in Hassan's building.

Neighbours also say Hassan had a "golden line" for electricity that meant his family's lights were always on, while other homes in the neighbourhood were in darkness.

The electrician called to fix any problems at the apartment says he knew Hassan over many years "but only from a distance". "[Hassan] was very strict - a military personality," the man says. "He was a butcher… He had no mercy."

The man told BBC News he had been in prison - not at Mezzeh but elsewhere - and was tortured there.

A local shopkeeper, Mohammed Naoura, says he didn't like Hassan but that you had to appear to support him.

"We are happy now," he adds. "Nobody believed this would ever happen."

Hussam Luka, head of the General Security Directorate (GSD), was less well-known among residents but had an apartment underneath Hassan.

His "ruthless, smooth-talking nature" reportedly earned him the nickname "the spider" - and he's under sanctions in the EU, US and UK.

A UK sanctions list says he was "responsible for the torture of opponents in custody", while the US Treasury Department says he "reportedly committed a number of massacres" while working in Homs.

The White House has said he is one of a small group of officials who might have information about missing American journalist Austin Tice.

At his home on Monday, rebels were dismantling furniture to be put into storage. They said they arrived after looters had already taken many of the most expensive items.

A photo of Luka and Assad remained, printed in different sizes and styles, alongside documents from security and intelligence events, and ceremonial medals and certificates from the foreign spy service in Russia - where the deposed Syrian leader Assad has fled.

"This award is to the coordinator of the mukhabarat [intelligence service] organ in the southern provinces of the Syrian Arab Republic," one certificate naming Luka says. "You showed the utmost professionalism and put in huge effort to fulfil the duties entrusted to you for the good of the Syrian people."

As rebels clear the apartment, a neighbour wanders in to see what's happening.

When asked what she knows about the regime official, she replies: "We keep to ourselves, they keep to themselves. No one in this building interacts with each other." She walks away.

In other affluent areas more homes have been abandoned. Fridges are fully stocked, wardrobes full and in some cases travel documents left behind.

The rebels who have taken over the homes are using them as bases, and say they are also preventing further looting.

At one lavish apartment, men say they are sleeping on blankets on marble floors beneath giant chandeliers and cooking on a camp stove in its modern kitchen. Guns are propped against plush sofas and arm chairs.

"We don't need any of this," a rebel says, gesticulating around the room.

At another, a child peaks through the curtain of a sprawling ground-floor apartment with an outdoor swimming pool. A large family say they are occupying the space.

Perhaps the grandest home in the area is the modern labyrinthine underground dwelling of one of the country's best-known businessmen - Khodr Taher Bin Ali, better known as Abu Ali Khodr.

Bin Ali has been sanctioned by the US, UK and EU for his role in supporting and benefiting from the Syrian regime.

His home has an elevator, a full-size gym, an indoor swimming pool, jacuzzi and sauna, and an industrial kitchen.

In the master bedroom, there are two golden safes, with space for dozens of watches - in a drawer there is a forgotten warranty card for luxury brand Audemars Piguet. A gun case and jewellery boxes in the wardrobe are empty.

The children's ensuite bedrooms still have toys and a Louis Vuitton handbag on the floor and homework and school reports are in the cupboards. A Quran rests on a countertop with the words "A gift from the president Bashar al-Assad" inscribed on the side.

Around the corner from Bin Ali is the home of Ali Mamlouk, one of Assad's closest associates and among the most senior and notorious members of the regime. He was reportedly given the nickname "black box" because of his control over sensitive information.

He was sentenced alongside Hassan by French judges this year for war crimes, and is also wanted in Lebanon for two explosions in 2012 in the city of Tripoli that killed and wounded dozens.

Like Luka, the White House believes Mamlouk is one of few men who could have information about Tice.

His home is padlocked shut, and rebels are more reluctant to grant entry there.

In a guard booth outside, there are notes on visitors to the property before Assad's fall - people delivering chocolates, water and vegetables, and coming to fix the electricity.

"No one could see, no one could walk, no one could pass by this area. It's actually the first time I'm seeing this place from up close," says 17-year-old Mo Rasmi Taftaf, whose family own a house nearby.

"Whenever he came in or out, guards would cut the roads off," one neighbour says.

Shouting down from a second-floor balcony, another gestures towards Mamlouk's large home when asked about the wanted regime figure.

"It felt like there was a strange atmosphere" on the street the night before news broke that Assad had fled, he says, without elaborating.

"His security was here at the time but I saw them leave on Sunday morning - a lot of cars. Ali Mamlouk wasn't here," he adds, before returning inside.

Another man, who declines to give his name, says he doesn't want to talk about the regime men.

"I just want to live in peace. I don't want to open this book or explore all of these crimes - there would be a lot of blood."

Many, though, do want justice.

The leader of HTS has vowed to pursue the senior regime figures in Syria and asked other countries to hand over those who fled. Those wanted elsewhere have limited places to run.

Finding the men will be a challenge.

"While there is no confirmed information on the current whereabouts of senior regime figures like Jamil Hassan, Ali Mamlouk, and others, there are concerns that such individuals could benefit from political deals that enable them to evade justice," the Syrian Center for Media and Freedom of Expression (SCM) tells the BBC.

"Some are likely to have sought refuge in allied countries, complicating future extradition efforts, while others may still be in Syria, living discreetly."

On Hassan's street, neighbours speculate about where the vanished war criminal has gone.

His family left few clues in the apartment. But in the office is a certificate for Hassan's daughter signed by Hassan Nasrallah, the late leader of Lebanon-based Shia militant group Hezbollah, thanking her for her "help and support for this honourable resistance".

Several neighbours suggest he may be hiding in Lebanon or has transited through there, while the local shopkeeper says he thinks Hassan headed for the coast, perhaps to Latakia in the north - the heartland of the minority Alawite sect to which Assad and many of his closest allies belong.

Meanwhile, Lebanese newspaper Nida al-Watan reports that Mamlouk was smuggled across the border and into the Lebanese capital Beirut by Hezbollah - a long-time ally of Syria's Ba'ath government.

Hezbollah has not confirmed offering assistance to any regime figures, and the Lebanese government has said no Syrian officials targeted by international warrants were authorised to enter through legal crossings. Lebanese security services say Mamlouk is not in the country.

Syrian-British barrister Ibrahim Olabi says regime officials may have acquired new identities and passports, as they were powerful people backed by state institutions.

When it comes to getting justice, he adds, a lack of evidence is not the problem. It is more about finding them and getting them to a place where they can be held accountable.

The SCM says doing this will "require considerable resources, sustained political will, and international collaboration".

Failing to do so will send a "dangerous message that crimes, including war crimes and crimes against humanity, can go unpunished", it adds.

Ibrahim Olabi says he is hopeful that justice will be served.

"It will absolutely be a hunt," he says, but "the world now is a small place through social media, private investigators, political leverages".

Hassan's neighbours who were willing to talk say they hope he will one day be returned to Syria, far away from their street, to be punished.