Speaking for the first time since the killing, Danielle Cable, 17, of Orpington, Kent broke down in tears as she told how the killer ignored her pleas and how her boyfriend Stephen Cameron died begging her to help him.
Danielle said she asked passing drivers to help as Mr Cameron was attacked last Sunday - but they all turned their backs on her pleas.
Ms Cable, a waitress, said: "We went to get some bagels. Steve wanted me to drive so we drove up the road and a car came from nowhere. "I had to brake sharply. We stopped at traffic lights and the other driver got out of the car. Steve got out to see what he wanted and he hit Steve.
"I got out and begged him not to hurt him. I was begging the other drivers to help. Everyone just ignored me."
She said that after her boyfriend had been stabbed, she held him in her arms. Steve called out 'Get the number plate'.
"He just looked at me. There was blood going everywhere. He was just looking at me and said 'Please help me', and there was nothing I could do. I was trying to get him to stay with me but it was just too late."
Ms Cable, who travelled to London yesterday with her parents, Jim and Mandy, from Swanley, Kent, was being comforted by her father as she relived the tragedy.
She said the killer had said nothing during the attack and when asked to describe the man, Danielle said: "He is a monster." She added: "This man has destroyed my life because Steve was my life."
Reliving her fiancee's last moments, she said she felt threatened as she got out of the car to help.
"I saw his knife and I was pleading with him not to hurt Steve. I couldn't go near him because I thought he'd hurt me. Steve was trying to kick the knife out of his hand and looking at me to say 'stay back'."
She said she had screamed for help from passing motorists, but to no avail. "They just sat in their cars and didn't do anything."
Asked what she would remember about Mr Cameron, Ms Cable wiped her eyes and said: "The way he looked at me and the way he always told me he loved me. I just wish he had stabbed me as well, so I could have died with him."
Ms Cable appealed to anyone with information to come forward and help catch the killer. "If they've got any small detail they can remember, just phone up," she said
Referring to a television broadcast of her interview scheduled to be transmitted tonight, she said: "I just hope he is watching this now and looking at my face, remembering that I was pleading with him not to kill the person I loved more than anything. He just looked at me like I was dirt."
Danielle's father praised his daughter's courage: "I think she has been very brave. We can't stop grieving until they catch this monster. They have just got to catch him as soon as possible before he does it again."
Asked what motive the killer could have had, Mr Cable said: "For what? Why did he do it? How could you kill someone like Steve?"Reuse content