According to an Israeli autopsy, all six people had been shot dead at close range, two to three days before the autopsy on Sunday.
The Israeli military found the bodies on Saturday afternoon.
Several of them would have been released in the event of a ceasefire agreement, says a high-ranking Hamas source to AFP.
Instead, they are being brought home to a country in mourning in body bags. Five of the dead were captured during Hamas' terror attack on the Supernova music festival on October 7 last year, the sixth was taken from a kibbutz.
The military claims that they were killed shortly before they were to be rescued by Israeli forces.
Apologizes
Israel's President Isaac Herzog apologizes on behalf of the state to the families for failing to bring them home safely, writes Haaretz.
One of the dead is 23-year-old Hersh Goldberg-Polin. He was both an Israeli and American citizen and appeared in a film clip published by Hamas in April, where he was seen with only one hand.
"It is with great sorrow and dismay that the Goldberg-Polin family announces that their beloved son and brother Hersh is dead", says his family in a statement.
Biden, who had a meeting with Goldberg-Polin's parents, says in a statement that he is "devastated" by the news.
Accuses Netanyahu
Around 250 people were taken hostage during Hamas' attack on Israel on October 7 last year. Before it was confirmed that six of them had been found dead on Saturday, Israel stated that it believes that 108 of the captives are still being held in Gaza and that around a third of them are no longer alive.
In total, over 40,000 people have been killed in Gaza since the start of the war, according to health authorities in the Hamas-controlled area. According to the UN, most of the dead are women and children.
Nearly 1,200 people, most of them civilians, were killed during Hamas' attack on Israel on October 7 last year, according to Israel.
