“He says he had a so-called blackout,” defence lawyer Rolf Knudsen told broadcaster NRK.
Knudsen said his client had no recollection of his movements over a period of several hours on New Year’s Day.
Hilda Feste was sexually abused that evening before being beaten to death in Os, western Norway.
“He says he had nothing to do with it,” Knudsen told news agency NTB after his client was taken in for questioning on Tuesday evening.
“He’s distraught and is taking this very hard. But he realizes it’s a serious case and wishes to cooperate with the police.”
Knudsen said the suspect has a job. His only previous convictions were for traffic offences.
At a press conference on Tuesday evening, prosecutor Asbjørn Onarheim said the arrest had been undramatic. The suspect is being held in custody in Bergen.
Onarheim said technical evidence had led police to the 18-year-old, who was questioned over the murder at a previous date.
“The accused was in for questioning in connection with the case and consented to give his fingerprints and take a DNA test. The reason the accused was questioned is that police had information about him being outdoors in Os on the evening of the murder.”
Police did not confirm if a DNA match had led to the arrest.
The deputy mayor of Os, Marie Bruarøy, said the town’s residents had lived in partial fear for the last two months.
“It’s certainly a relief if the culprit isn’t on the loose anymore,” she told NRK.
Bruarøy said she was shocked that the suspect was so young.
“It’s a strange feeling. The arrest was a shocking piece of news, while also coming as a relief. I’d imagine this is going to affect Os for a few days.”
A phone operator in Hamarøy in the north of the country, was the first to realize that Feste was in distress after the 98-year-old set off her emergency medical alarm.
Since the alarm allows for two-way communication, the operator heard what was happening in the apartment, newspaper Bergens Tidende reported.
According to alarm operator service HT Safe, and officials from Os council, the operator placed a call to the town’s home-care service after failing to establish verbal contact with Feste.
The home-care nurse on duty in the building next door to the Feste’s was then sent to the woman’s apartment at the Oshaugen care facility.
When the care worker looked through the window and saw the woman being attacked, she retreated to a safe location and notified the police.
The nurse then phoned two of her colleagues who were working nearby. Together, the three of them entered Feste’s apartment, where they found the 98-year-old woman suffering from massive head injuries.