13/06/2014 10:06 BST | Updated 13/08/2014 06:59 BST

Catalina: A Young Life Lost in the Tunnels of Bucharest

The last time we met her had been underground, deep in the Bucharest tunnel system that Bruce Lee and his gang of homeless drug addicts call home.

Catalina had been perched on one of the heating pipes in front of an icon of the Virgin Mary, a ring of infected syringe sores around her neck a jagged reminder of her drug-addicted life in the sewers. 'This is where I destroyed myself' she had told us that day, prophetically.

She featured as one of the main characters in our film broadcast on Channel 4 News last month. A story that has shocked over two million people who have viewed it around the world and has ramped up the pressure on authorities charged with managing Romania's homeless youngsters.

But it is too late for Catalina. She is dead. She collapsed and died in the tunnels last week after suffering from AIDS, chronic pneumonia and heart failure which cut short her painfully short life. She had just turned 18.

For a feature appearing on Channel 4 news tonight, we were invited back to Romania and to her wake. We were ushered through the cobble stones and courtyard, past children playing in the dust and adults weeping by the door of the tiny tin roofed shack. Catalina lay in the open casket veiled in a bridal gown, as is custom for Roma girls who die before their wedding day. A priest stood to one side, chanting prayers as her sisters stood over her, fussing over the veil, or rearranging her beloved pink cd player that they had stuffed under her pillow, music to keep her company in the grave.

As the candles flickered late into the night, Catalina's friends began to arrive in the house, familiar faces from her home in the tunnels coming to pay their last respects.

We found Eliza, one of Catalina's best friends whom we filmed joking around in the tunnels weeks earlier. "We met in a foster house named Pinocchio. I hanged out with her everywhere. She was like a sister to me," she told us tears streaming down her face.

One of five siblings born into acute poverty, Catalina's parents had abandoned her as a baby, sending her to live in a children's institution called Pinocchio's on the edge of Bucharest, for the first years of her life. It was a factor we were told later by the head of the institution that had impacted deeply upon her life, a lifetime lacking in love that had drawn her deeply into life within the sewers. Bruce Lee and the tight knit gang underground, she said, had become the family Catalina had never had.

"For her getting some attention was an extraordinary experience," said Carmen her sister "because now she felt valued in those moments. She was happy if anybody was looking out for her or giving her any attention," she said.

The procession of mourners continued to stream in, silent faces, clutching her hand, kissing her forehead, whispering their goodbyes.

The following morning, the day of Catalina's funeral, it was the turn of Bruce Lee - the self-styled "King of the Sewers". Never shy of a spectacle, he arrived barefoot with his head painted in Aurolac, a luminous helmet of bright silver paint that the addicts sniff. A stark reminder of the crazed drug-infested atmosphere where Catalina had died.

A window was removed from the house and the coffin was pulled out amidst wails and mournful chaos. Carried in the back of an open transit van, a small gaggle of mourners led a slow march to the Gare Du Nord, stopping at the sewer entrance, the hole she had once called home.

The same sewer entrance we had disappeared into weeks earlier, appears empty. Nobody stirred until her sister wails down into the tunnel: "Catalina is here, this is where she lived with you, come and see her for the last time."

Gradually they begin to emerge, weary-eyed in the bright light above ground, clutching Aurolac bags to steady their nerves. A gaggle of sick and destitute individuals who have lost their way, gathering around the body of one of their own who had lost her life.

We followed the group to the funeral where Catalina's coffin was lowered into the ground. A small crowd surrounded her coffin, weeping and placing flowers over the casket. Her family she was torn from as a baby and the homeless family that had welcomed her in - briefly united in a moment of tragedy.

The next day we interviewed Cosmina Nicolescu, the Director General of the Social Assistance in Bucharest who told us: "For them life no longer matters. They are outcasts, renegades that are avoided and they are primarily lacking love and understanding. It wasn't their fault that they were born into this situation, or that they ended up in this situation."

We asked why more wasn't done to intervene before Catalina's death: "As far as we know from the tunnels she didn't want to be brought in the daylight. Her dying wishes, to die in the place where she had found family."

Cosmina says that they can't close the tunnels, for fear of pushing the vulnerable people who find sanctuary underground, into ever-more precarious places and situations. But she claims that Bruce Lee is banned from Bucharest, and has been removed several times before by the police. He just keeps on returning faster than the police return to take him away.

Today the tunnels alongside Bucharest's central station remain open for both business and sanctuary, attracting youngsters like Catalina, who struggle to exist at the very bottom of Romanian society. Drug addiction and premature death the price paid for those who choose to live underground.

Watch: 'Is death the only escape from life in Romania's tunnels' tonight on Channel 4 news at 7pm