After the cable car accident on Lake Maggiore, the only survivor, a six-year-old boy, was brought to Israel from Italy.
The circumstances of the trip were initially unclear.
Italian media reported unanimously on Sunday of a “kidnapping” after the orphan was not given to his father's aunt, the judicially ordered guardian, as agreed on Saturday by his grandfather after a visit.
"The boy was brought to Israel by his grandfather, against the will of the legal guardians and despite the court's ban on leaving the country," said Massimo Sana, the aunt's lawyer, of the German Press Agency on request.
The public prosecutor's office in the northern Italian city of Pavia is already investigating kidnappings.
At the same time, international regulations would be examined to bring the boy back to Italy, added the lawyer.
Diplomatic channels have also been activated.
Relatives fight for custody
"We brought Eitan back home," said Gali Peleg, the sister of the boy's mother, who was killed in the accident on May 23, to the Israeli radio station 103FM on Sunday.
The background to the action over the weekend is a dispute between the boy's relatives who are claiming custody.
The child had lost both of his parents and his brother in the crash of a cable car gondola on Pentecost Sunday.
A total of 14 people were killed in the accident in Piedmont.
A court then appointed the father's sister, who lived in Pavia in the Lombardy region, as guardian.
"We didn't kidnap Eitan, we won't use that word either," said Gali Peleg, the mother's sister. The Israeli Foreign Ministry examined the case on Sunday. There was initially no official information from the authorities in Italy.