The naval ship did come, but survivors say it was about 30 minutes after spotting them after scores of passengers had already died

A prosecutor in Sicily confirmed this week that he'd begun an investigation into allegations that a U.S. Navy ship appeared to have initially ignored cries for help from migrants aboard an inflatable raft off Libya—a delay that may have led to the deaths of 76 people including a baby.

"If the first time we had seen the ship, if it had come and helped us, there wouldn't have been deaths," charged one of the survivors.

Survivors described the events of the June 12 shipwreck in harrowing details in a video published by Italian news site La Repubblica.

Sailors from the Spearhead-class expeditionary fast transport ship USNS Trenton providing assistance to mariners in distress that they encountered while conducting routine operations in the Mediterranean Sea, June 12, 2018. (U.S. Navy photo/Released)

"We saw the American ship," said one survivor referring to the USNS Trenton. Several said they were close enough to see the American flag on the ship, adding that the sight of the vessel brought a sense of relief as the small dingy had begun to take on water. Trying to get the Trenton's attention, the migrants stood up, waved their shirts in the air, and called out.

But the U.S. Navy ship, according to survivors, did not approach them, but rather appeared to be moving further away even as the migrant ship tried to follow it.

The U.S. Navy and aid groups acknowledged that the ship ultimately did come to provide aid, helping 41 of those still alive.

But survivors say the relief came only when the ship came back around, some 30 minutes later. That was 30 minutes too late, as the boat had capsized and people were drowning.

"At that moment, I lost my only brother and my sister," said one woman, adding that she too almost lost her life.

"We clearly saw the same American ship that had ignored us approaching," the Guardian reports one man as saying in the video.

When they asked the people on the U.S. ship why they didn't help at first, survivors said they were told rescuing people was "not their job." The U.S. Navy had asserted in a statement about the rescue of the 41 people that it showed "our ability to respond rapidly to provide relief."

According to the International Organization for Migration, those aboard the ill-fated raft were mostly sub-Saharan Africans. It added:

they had left Zuwara, in Libya, during the night of 11 June, sailing on a dinghy carrying 117 people, including 20 women and a one-year-old child. After seven hours of navigation, the boat began to deflate and many migrants fell into the water. The U.S. Trenton, patrolling nearby, intervened and managed to bring 41 people to safety. Overall, 76 migrants lost their lives, survivors said, including 15 of the 20 women and the one-year-old child.