An American suspect in the case again proclaimed her innocence in the same hearing.
"It was expected" that prosecutors would seek a harsh penalty, said Valter Biscotti, a lawyer for Rudy Hermann Guede, the Ivorian accused in the case.
At his lawyers' request, a fast-track trial is being conducted for Guede. He has acknowledged being in the bedroom where Meredith Kercher's body, stabbed in the neck and lying in a pool of blood, was found in November 2007 in the house she rented with American student Amanda Knox, 21.
Fast-track trials can sometimes result in lighter penalties. But prosecutors asked the court Saturday to convict Guede and mete out Italy's stiffest punishment - life imprisonment. Italy does not have the death penalty.
The case has received heavy publicity in Italy, in Britain, and in the United States, where Knox is a University of Washington student.
The court deciding Guede's fate is also hearing arguments to determine if Knox and her former boyfriend, Italian student Raffaele Sollecito, should stand trial for the slaying. A ruling on prosecutors' request for their indictment is expected toward the end of October.
All three suspects have repeatedly denied wrongdoing in the slaying, which took place in Perugia, a university town which a large foreign student population.
Knox again proclaimed her innocence in court Saturday.
She asked permission during the closed-door hearing to make a declaration in English, the Italian news agencies ANSA and Apcom reported from Perugia. In remarks that were translated into Italian, she told the court, "I am innocent," the reports said.
Sky TG24 TV, without citing sources, said Knox cried as she spoke and contended she had been pressured by police during interrogations.
Italian TV showed a brief, partial view of Knox as she given a microphone to address the court. Only her hands, busily gesticulating as she addressed the court, could be seen. There was no audio.
Knox and Sollecito have been jailed as suspects since shortly after the slaying. Under Italian law, they can be jailed for as long as a year during the investigation.
Knox and Sollecito, 24, have given conflicting statements.
Sollecito has said he was at his own apartment in Perugia. He said he does not remember if Knox spent the whole night with him.
Knox has insisted she was not at home during the slaying. But at one point, she also told prosecutors she was in the house the night of the slaying and covered her ears to muffle Kercher's screams while a Congolese man who owns a pub in the town killed Kercher. The Congolese man was initially jailed, but authorities released him, saying he was no longer a suspect.