Gaza (CNN) -- When Jwdat Abu Ghrb spotted a dark shape last summer in the waters off Gaza, where he was diving for fish, he initially thought it was a corpse.
"I was afraid," he told CNN. "I put on my goggles, dove underneath and still couldn't tell what it was. I resurfaced and got some help from other people and family members and came back, and after full four hours of trying we managed to get it out of the water and I was shocked by what I found."
It was a life-size bronze statue, believed to be a 2,500-year-old depiction of the ancient Greek god Apollo.
He described the half-ton object as "treasure pulled out of the sea."
"I thought it was made of gold; I was going to be rich," Ghrb said. "So I took it home to hide it." But then others got involved. A local armed brigade took control of the statue, and someone listed it for sale on the online auction site eBay, with a starting price of about $500,000, according to authorities.
The posting raised suspicions among officials in the Ministry of Tourism and Antiquities and the Interior Ministry in Gaza, which is governed by the Palestinian Islamist group Hamas.
The antiquities authority and the Interior Ministry opened an investigation into what they said they suspected was an illegal attempt to sell the work of art.
"It is against the law to sell an artifact found in the Palestinian territories and Gaza in an illegal manner," Ahmad Al-Burch, head of the antiquities department at the Ministry of Tourism and Antiquities in Gaza, told CNN.
He said the case was being handled by the Ministry of the Interior, while the antiquities authority looks after the statue.
Authorities there asked that the statue, as a historical artifact found in Gaza, be handed over; they have hidden it from public view.
But in a Gaza gold store, a man who displayed video of the statue told CNN that he has custody of it and that it is in safe hands, but -- if someone wants to buy it -- that would be possible.
Government officials promise that the statue will not be sold and that they will start restoration and display it after an investigation into its discovery is completed.
"We are not denying that the statue was found in the sea -- as a matter of fact, that is a very authentic and real story," Al-Burch said.
A green spot -- a sign of decay -- has formed on the leg of the statue, which is exposed to the air.
"We are trying to preserve the statue to show it for the public in the near future."
He said the antiquities authority was working on a plan for the statue to be displayed in world-class museums around the world.
Museum authorities in Geneva, Switzerland, have offered to help repair and preserve the statue, and plan for its eventual display in Gaza, he said.
For Ghrb and his family, the discovery seems unlikely to land them the financial security they had hoped for with a sale. They are instead hoping to net a reward for the find, which has excited archaeologists around the world.
CNN's Kareem Khadder in Jerusalem and Laura Smith-Spark in London contributed to this report.