Greek authorities have arrested an Afghan national in connection with the death of a Scottish woman whose body was found in a suitcase in an abandoned building in central Athens.

Elisabeth-Jane Ross, 38, a charity worker described as an “angel full of innocence and goodness” by friends, had been in Greece for almost three weeks when she is believed to have died.

Police sources said the suspect was a 26-year-old Afghan citizen who had allegedly confessed to the crime. He had been brought in for questioning by Greece’s homicide division last Thursday, two days after Ross’s body was publicly identified.

A statement released by police on Sunday said: “A criminal file has been opened against a 26-year-old foreign national for intentional homicide, robbery and violation of the law [regarding] weapons.”

Explaining the accusation of ownership of illegal weapons, security officials said “various arms – some real, some fake” had been discovered in the suspect’s home, also thought to be in the downtown area of Kypseli where the body was discovered.

He is expected to be charged on Monday.

Throughout the investigation, Greek authorities had worked closely with the UK’s National Crime Agency (NCA) and Police Scotland, according to the statement.

Ross, who had strong links with the charity sector in Greece, is the daughter of a prominent lawyer in Edinburgh, where she also lived.

She was reported to have friends in Kypseli, where her body was discovered on 18 July by a homeless man in what had once been a car park. Wrapped in cloth, it had been placed in a suitcase left in a decrepit, rubbish-strewn building at the site.

Sources told the Guardian that the suspect’s alleged use of credit cards that belonged to Ross had contributed to police identifying him.

“He was caught on camera withdrawing money with the cards from various ATMs,” one said. “The credit cards belonged to Ms Ross. That played a big role in leading us to him.”

For days, investigators were unable to make headway, citing the lack of fingerprints or DNA on the suitcase. Adding to the mystery was the discovery that her mobile phone had been used until the time when the body was publicly identified last week.

Police had described text messages sent to her father and other members of her family as deliberately misleading. The messages had spoken of her “need to be alone”.

The Briton’s “dispersed movements” in the days leading up to her death had made the quest to track her killer even harder.

After leaving the home of close friends in Keratsini, a suburb close to the port of Piraeus, where she had stayed for two weeks after flying to Greece, she had gone her own way, renting an apartment in the district of Exarchia in downtown Athens.

Greek media outlets reported the suspect had been found in possession of the keys to the rental apartment and that he was “the partner” of one of the Briton’s friends.

“As confirmed, the victim arrived in the country on June 26 and stayed at the home of friends until July 10, from where she departed to an unknown [address],” the police statement said.

The homicide division said it had made the announcement after amassing evidence that proved the Afghan had “placed the body in the case and carried it to the abandoned car park” in Kypseli.

Analysis of CCTV footage had played a role.

“The subsequent preliminary investigation … using investigative material and digital analysis of video footage, proved the involvement of the 26-year-old foreign national in the incident. [He] was brought in [for questioning] on 30 July and confessed to his actions,” the statement said.

It remains unknown how Ross died. Media reports quoted the suspect as telling police that when he visited the flat in Exarchia he had discovered her lifeless body in the bathroom.

An initial on-site postmortem showed there were no evident signs of injury or struggle on the Briton’s body but proved inconclusive because of advanced decomposition. Authorities have fast-tracked toxicological tests and analysis of vital organ tissues to determine the cause of death.

Grigoris Leon, who heads the Hellenic Society of Forensic Medicine, told the Guardian that examination of the lungs and eyes would help provide answers and determine “whether she had died a natural death”.

As tributes have poured in, flowers have been left beside the abandoned lot in Kypseli. One note read: “Here lies an angel.”

One friend in Edinburgh agreed with that, saying: “We have lost an angel, an angel full of innocence and goodness who only wanted to help people wherever she went.”The UK Foreign Office previously said: “Our thoughts are with Elisabeth’s family during this difficult time. We are providing consular support and are in contact with the local authorities.”

A Police Scotland spokesperson said: “We are aware of the death of a Scottish woman in Athens and are liaising with authorities in Greece. Officers are providing support to her family in Scotland.”