“His desperate attempt to call 999 before he lost consciousness, the panic he must have felt when he realised what was happening, the loneliness of dying in the street without a single person who knew his name; these things will haunt me forever, but Sam actually went through them.
“And for what?
"I think we have all come to realise that time simply gives you the means to learn how to pretend that everything is okay.
“Life forces you to carry on and be "normal".
“Even wonderful things that have happened since Sam was killed have a bitterness surrounding them, like the new babies that have been born into his family that will never know him, the celebrations that have happened with a piece missing.
"Sam was studying history and politics and would have been an amazing teacher.
“He never felt that he was better than anyone else; he was friends with people from every walk of life.
“Everyone who knew Samuel is so proud to have known him and shared a part of his life.
“I feel so privileged to have been able to say "I love you" and hear him say it back.
“Now we direct those words to a hole in the ground and hear nothing but silence in response.
“He was 24 years old.
“There will never be a time that I stop dreaming of seeing that smile again."
Samuel's mother and father, Sarah Guidera and Chris Guidera (pictured above), said: "From the moment Samuel was murdered on February 12, 2011, we as his parents started a life sentence from which we will never be released.
"We still feel a sense of anger and all we can do is continue to cope with each day as it comes, with the help of medication, family, friends, whatever it takes.
“As parents we have seen the devastation and heartbreak it has caused Sam's brother and sister, other family members and friends.
“We just want somebody out there who knows something that could help in the apprehending of the killers to come forward so they do not have the opportunity to take another person's life and destroy another family.
“It could be somebody reading this who gets the call about the savage death of a loved one next.
"So we miss and think of him so much every single day, we cry, we love him so much.
“Time is not a healer, we will never get back to normal; the people we were before no longer exist.
“So please look at your son, brother, uncle, think how you would miss them and if you know anything come forward; don't let the cowards who took my son's life kill again."
Detective Chief Inspector Chris Jones: "Whilst two years have passed since the murder of Samuel Guidera, the Met Police remains committed to identifying and bringing to justice those responsible.
“I am convinced there are persons within the community who for reasons, be it family or other loyalties, have yet to come forward with the information they have.
"I would ask them to consider the devastating impact Samuel's death continues to have on his family and loved ones and appeal for them to contact the investigation team.
“The Met continues to offer a £20,000 reward and I would stress any person coming forward will be spoken to in confidence with all measures to protect their identity and safety considered."
Anyone with information is asked to contact the incident room on 020 8345 3734; or Crimestoppers anonymously on 0800 555111.
In February 2011 police arrested a 39-year-old man in Penge and an 18-year-old man in Sydenham on suspicion of murder.
The next month they arrested a 28-year-old man in Sydenham in connection with the inquiry.
And in January last year officers arrested a 21-year-old man on suspicion of murder.
All four were bailed pending further enquiries and subsequently released with no further action.
Samuel Guidera murder: Family appeal to catch University of Greenwich student's killer
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