Who will miss Perugia's lost boy as the Kercher case moves on?

Amid all the mystery and doubts over the gruesome death of the British exchange student Meredith Kercher in Perugia a year ago, Rudy Guede is the single relatively fixed point. The 24-year-old, born in Ivory Coast but raised in Italy, last week began a 30-year sentence for her murder.

Guede is the only one of the three people charged with Kercher's murder to admit to having been in the flat when she died. He heard her screams, he saw her blood splattered about, and he could not get the sight out of his mind. "When I closed my eyes, I could only see red," he wrote in an account for the police after his arrest. "I have never seen so much blood. All of that blood on her beautiful face."

Yet in court he claimed he did her no harm, saying he was in the lavatory the whole time. Few believed this story, however, and at the end of his fast-track trial on Tuesday, Judge Paolo Micheli sentenced him to 30 years – less than the life sentence prosecutors demanded, but a heavy penalty nonetheless. His lawyers have announced that he will appeal.

The early sentence for Guede was just one of the many stark contrasts between his circumstances and those of Raffaele Sollecito and Amanda Knox, the privileged pair who go on trial for their alleged part in the murder next month. Guede was five when he left Ivory Coast with his father, Pacome Roger Guede, bound for Europe. They settled in Perugia, where Pacome worked on building sites, but after a decade he went home, leaving behind his son, now a teenager.

Guede, tall, thin and athletic, was a gifted basketball player, and Paolo Caporali, a wealthy local man who sponsored the town's youth team, informally adopted him. But Guede was already on the slide. He dropped out of school, dabbled in drugs and showed little ambition. "He preferred to spend the day in front of the television or with video games," said Caporali. "He had little wish to study, and even less to work." Rumour had it that he dealt in drugs, molested girls and dipped into their handbags.

When Guede moved to Milan, Caporali gave him a job as a gardener at a farmhouse B&B he ran there, but he rarely showed up, and in August 2007 he was sacked. Now homeless and jobless, his descent was fast. Three times before Kercher's murder, he was caught breaking into private premises. Four days before Halloween, police found him in a primary school in Milan, armed with an 11in knife.

Since the only clear forensic evidence in the case implicated Guede, most prosecutors might have concluded that they had done their job once he was convicted. But next month, the court will hear the state's claim that Guede came to Kercher's apartment with her flatmate, Knox, and Sollecito – two people he barely knew – and that all three had a premeditated determination to kill the English girl as the culmination of a Halloween rite. It remains to be seen if this lurid theory will prevail over Sollecito's more prosaic defence: that Kercher returned home early on the night of 1 November 2007, saw that Guede had broken in, and died at his hands alone.