The prime minister apologised on Thursday as the Ministry of Oceans and Fisheries was found to have concealed the discovery of a human bone fragment from the Sewol ferry until after the joint memorial service of five missing victims.

A search team under the ministry found a piece of human wrist bone from the sunken ship last Friday, a day before the memorial service, but its chief Kim Hyun-tae decided to keep it a secret in a suspected bid to prevent additional search. The five missing victims’ families had decided a day earlier to give up finding the remains.

Kim has been removed from his duties and is under investigation.

“The concealment of the remains of a Sewol victim was beyond disappointment for the bereaved families and the Korean people. It gave them a sense of betrayal. What happened was shameful, with no room for excuse,” Prime Minister Lee Nak-yon said during a weekly policy coordination meeting.

“We offer our deepest apologies to the families of the deceased and the people.”

Lee said the government will conduct a swift investigation into the matter and reprimand those responsible for the concealment.

“This incident is a bitter warning that there is a tendency for complacency and irresponsibility in public service,” Lee said.

“We will once again strengthen efforts to tighten discipline of public officials and raise their sense of responsibility.”

Oceans Minister Kim Young-choon also apologised in a statement, saying the ministry will review the entire search process.

The Sewol ferry sank on April 16, 2014, in waters off the country’s southwestern coast, killing 304 people, mostly teenagers on a field trip, in one of the worst maritime tragedies in South Korean history.