A day of celebration ended in tragedy after officials say a “catastrophic failure” led to a dock gateway collapsing on a small Georgia island.

National civil rights attorney Ben Crump is demanding a federal investigation into the deadly dock collapse on Sapelo Island this past weekend. Crump is representing the families of three people who died and one person who was hurt. Investigators are still working to figure out why the ferry deck collapsed on Saturday.

Authorities are working to identify the cause of a partial ferry dock collapse on Georgia’s Sapelo Island that turned a day of celebration into tragedy, leaving at least seven dead and six critically injured as crowds gathered for a cultural festival.