TEL AVIV, Israel (NewsNation) — Hamas has returned the remains of the last American still a hostage following the Oct. 7, 2023, attack on Israel.

Israeli American tank commander Itay Chen’s body was returned as exchanges outlined in the fragile ceasefire went ahead despite allegations of violations on both sides.

His family mourned after being notified of Chen’s return, which they called “bittersweet,” and demanded further inquiry into how the attack was able to happen, according to a statement from Israel’s Hostages and Missing Families Forum.

The exchanges are the central component of the initial phase of the U.S.-brokered agreement that requires Hamas to return all hostages’ remains as quickly as possible. The exchanges have gone ahead even as Israel and Hamas have accused each other of breaching other terms of the deal.

Officials at Gaza’s largest functioning hospital, Nasser Hospital in Khan Younis, said Wednesday that the bodies of 15 more Palestinians were returned.

Israel has not disclosed how many bodies it is holding or where they were recovered but has been returning 15 each time the remains of an Israeli hostage are returned from Gaza.

Hamas returned 20 living hostages to Israel on Oct. 13. The group has since also returned the remains of 21 bodies. Israeli officials have decried parts of the process as a violation of the agreement, accusing Hamas of handing over partial remains in some instances and staging the discovery of bodies in others.

The International Committee of the Red Cross has transported 285 bodies held in Israeli custody to Gaza since last month’s agreement was brokered, though health officials in Gaza have said identifying the remains is complicated by a lack of DNA testing kits.

Health officials in Gaza have struggled to identify the bodies without access to DNA kits and have identified 84 of the bodies.

The Associated Press contributed to this report.