Italian prosecutors have launched an investigation after a six-year-old boy who was the only person to survive a cable car crash in Italy in May was taken by his grandfather to Israel, against the wishes of other members of his family amid a bitter custody battle.

Eitan Biran, whose parents and two-year-old brother died in the Stresa-Mottarone aerial tramway crash on 23 May, has been at the centre of a custody battle between relatives in Italy and Israel.

Eitan, whose parents were Israeli nationals resident in Italy, had been living with his paternal aunt Aya Biran-Nirko in Pavia before his alleged abduction on Saturday. Biran-Nirko was granted custody of the child after he was discharged from hospital in Turin in June. Gali Peleg, Eitan’s maternal aunt in Tel Aviv, last month began an adoption process, with her lawyer claiming the child was being held hostage.

She told Israel’s Radio 103FM on Sunday: “We did not kidnap Eitan and we will not use that word. We brought Eitan back home. We had to do it after we received no information on his health or mental condition. If the judge had not scheduled meetings [with the child], we would not have seen him.”

Eitan’s maternal grandfather, Shmulik Peleg, moved to Italy from Tel Aviv after the crash. According to reports in the Italian press, Peleg took the child out on Saturday morning but did not bring him home by 6.30pm as agreed. After the alarm was raised, Italian police found Eitan had left Italy onboard a private plane with Peleg, who was in possession of the child’s Israeli passport. Diplomatic sources later confirmed their arrival in Israel.

Italian media reported that Biran-Nirko had repeatedly sent messages to Peleg, who is claimed to have eventually responded: “Eitan has returned home.”

Armando Simbari, a lawyer representing Biran-Nirko, told Corriere della Sera: “The news is upsetting for everyone and creates a lot of concern. He [Eitan] was snatched from the family he grew up with, and from the doctors still treating his trauma.”

Eitan’s great grandparents also died in the crash, which is believed to have happened when a lead cable snapped, causing the cabin to hurtle backwards before falling about 20 metres into a wooded area below. The cabin was just a few metres away from Monte Mottarone, its destination almost 1,500 metres above sea level, when the crash happened. Fifteen people had boarded the cable car in Stresa, the town below, next to Lake Maggiore, for the 20-minute ride. Eight of the 14 who died, including a six-year-old boy, were Italian nationals. The other victim was an Iranian national who lived in Rome.

Investigators are still working to establish the cause of the crash. The cabin’s “black box” was recently removed from the crash site. It is expected to take three months to assess whether information contained in the software will indicate anomalies in the cable car system. Fourteen people from the company that built and maintained the cable car system and the firm that managed it are under investigation.

Prosecutors claimed a few days after the crash that the emergency brakes, which ought to have prevented the cabin from falling backwards when the lead cable snapped, had been deactivated in order to avoid disruptions to the service.

The Stresa-Mottarone service had resumed in late April as Italy eased coronavirus lockdown restrictions. Investigators said in late May that technical checks were done, including one on 3 May to “remedy inefficiencies”, but had not been “decisive” in resolving issues.

In June, Italy’s public broadcaster, Rai, was criticised for broadcasting leaked CCTV footage of the crash, which was Italy’s worst cable car disaster in 20 years.

Twenty people died in February 1998 when a US military aircraft that was flying too low sliced a cable supporting a cabin near the Dolomites ski resort of Cavalese. In 1976, 41 people died in an accident affecting the same cable car system.