Olindo Romano, 45, and his wife, Rosa Bazzi, 43, are accused of stabbing to death Raffaella Castagna, her two-year-old son Farouk, her mother, Paola Galli, and another neighbour, Valeria Cherubini.
The prosecution alleged that the couple had burst into the house in the town of Erba near Como, armed with knives, following a row Bazzi had had with Ms Castagna over the noise her son was making.
After stabbing their victims to death, they set fire to the flat in an attempt to destroy evidence before calmly going for dinner in a nearby pizzeria to construct themselves an alibi.
The prosecution said that, in a call intercepted by police after the killings, Bazzi told Romano: "See how well we are sleeping now?"
The key prosecution witness is Ms Cherubini's husband, Mario Frigerio, who survived the knife attack and was thus able to identify Romano and his wife as the killers when he was interviewed in his hospital bed by detectives.
The murders, which took place just two weeks before Christmas 2006, caused shockwaves throughout Italy and at first Ms Castagna's husband, Azouz Marzouk, a Tunisian drug-dealer, was said to be a suspect.
However, after Mr Frigerio's revelations and subsequent DNA finds, as well as confessions – which have since been retracted – Romano and Bazzi were charged with murder.
Yesterday, the trial opened at a Como court in front of a packed public gallery, with tickets for admission to the courtroom said to be changing hands at 100.
The prosecutor, Massimo Astori, said: "On those corpses are the signatures of the accused and I will demonstrate this with irrefutable evidence.
"Nothing will remain in the dark, everything can be proved. All this took place in a matter of minutes, five people cut down but one of whom managed to survive.
"Scientific facts and logic will prove that this was nothing but premeditated murder, as the victims had been followed and watched," Mr Astori went on.
"They were also careful never to talk about the crime on the telephone in case they were heard by investigators – apart from one chilling phrase Rosa used: 'See how well we are sleeping now?'.
Mr Astori said he intended to call 53 witnesses and that he would also be using the five cases of complaints about noise that Romano and Bazzi had filed against Ms Castagna in the weeks leading up to the murders.
He added that he would also be using confessions the couple had made on tiny notes found in a Bible and a book on Pope Benedict XVI that had been found in the cells of the accused.
Sixty members of the public were allowed into the courtroom for the hearing. Many of them said they had arrived early to beat the rush and guarantee themselves one of the tickets that were issued by court ushers.
Giuseppina Rossi said: "I was up early to make sure. I got the first bus from my village to Como at 5am. It's only half an hour away but I didn't want to miss this and there was no way I was going to pay a tout 100.
"It made me sick to see Romano and his wife in there, holding hands and whispering to each other like two love-birds," the pensioner added.
"If I had my way I would put them both against the wall and pull the trigger."
Many in the public gallery gasped in horror as the prosecutor described how all the victims had suffered "numerous knife wounds to their throats, chest and stomach".
Romano and his wife are sitting together in a metal cage to the side of the court, and during proceedings yesterday they continually shook their heads and said: "Lies, all lies."