(CBS/AP) PERUGIA, Italy - A key prosecution witness testifying in Amanda Knox's appeals trial gave conflicting reports Saturday about whether he saw the American near the crime scene the night her British roommate was murdered.
The contradicting testimony and confused dates offered by Antonio Curatolo, a self-described drug addict and homeless man now in prison for an unrelated conviction, cast doubts on his credibility. The defense called him flat-out unreliable, while the prosecution maintained that, despite some lack of precision, the witness was lucid and clear in what he remembered.
Knox, 23, was convicted of the sexual assault and murder of Meredith Kercher in the house they shared as exchange students in Perugia and is serving a 26-year-prison sentence.
In the first trial, Curatolo placed Knox and her co-defendant and ex-boyfriend, Raffaele Sollecito, in a square near the house on the night of the murder. He said the two were chatting and added that he remembered seeing buses in the square. The testimony was important because it directly contradicted Knox and Sollecito's claim that they were at Sollecito's house the night of the murder.
On Saturday he repeated that he saw the two "talking excitedly" in the square and said he thought it was Halloween night -- which would be the night before the Nov. 1, 2007 murder. He was unclear when Halloween night actually is, saying he thought it was Nov. 1 or 2. Despite the date confusion, he repeatedly said that he saw young people dressed up in costumes.
But, at another point, he also said he clearly remembers seeing police at the house the morning after he saw Knox and Sollecito in the square. Police went to the crime scene on Nov. 2, when Kercher's body was found, stabbed to death and lying in a pool of blood.
"Police and Carabinieri were coming and going, and I also saw the 'extraterrestrials' -- that would be the men in white overalls," Curatolo told the court with a smile, referring to forensic experts gathering evidence.
Twice he was asked by Prosecutor Giuliano Mignini whether he was certain that police were at the house the morning after he saw Knox and Sollecito in the square. Curatolo answered: "I'm as certain as I am that I'm sitting here."
He said that in 2007 he was living outdoors in the square in question.
The 54-year-old also admitted to a long-lasting drug habit, including in 2007, saying: "I have always done drugs, ... heroin, which is not a hallucinogen." He also appeared to either lie or be confused when he initially told the court that he was currently living in a home. Pressed, he acknowledged he was in prison.
Curatolo has been convicted on a drug-dealing charge, said his lawyer, Fernanda Cherubini.
Escorted by police but not handcuffed, Curatolo entered the courtroom in Perugia using a crutch, his white hair unkempt.
The defense had long sought to discredit him.
Giulia Bongiorno, a lawyer for Sollecito, said the hearing "marked an important step forward for the defense's arguments."
Chris Mellas, Knox's stepfather, said that "it couldn't go any better today."
"He confirmed that there were disco buses and that he saw the kids getting on and that it was Halloween. Perfect!" Mellas said after the hearing.
The bus detail is relevant because on Oct. 31 several shuttle buses took people to clubs around Perugia for Halloween parties, while the following night discos were either closed or had a slower night. The prosecution, however, maintains that even on Nov. 1 tourist buses, public transport and possibly shuttle buses for some discos could have been operating.
Prosecutors insisted Curatolo remained reliable, if not very precise.
Prosecutor Manuela Comodi said the confusion between Oct. 31 and Nov. 1 is a moot point as it has already been ascertained that Knox was somewhere else -- in a pub where she worked -- on Oct. 31 and so could not have been seen in the square.
"What's certain is that she couldn't have been there on Halloween night," Comodi said. "There is no such thing as a perfect witness, save for one who has seen the crime. What matters is that a witness doesn't lie, and why should Curatolo lie?"
Francesco Maresca, a lawyer for the Kerchers who are civil plaintiffs in the case, told reporters that Curatolo was as reliable now as during the first trial. He noted that Curatolo said it was not raining when he saw Knox and Sollecito, which would confirm Nov. 1 since it wasn't raining that night but it had been raining on Oct. 31.
Knox and Sollecito have been behind bars since November 2007. Sollecito, who turned 27 Saturday, was also convicted of murder and sexual assault and sentenced to 25 years in prison.
The next hearing is on May 21, when experts reviewing DNA evidence will report their findings to the court.
Knox's young sister Deanna, who arrived in Italy this week, also attended the session.