An inquest will be held into the deaths of three sewer tunnel workers killed in a powerful methane gas explosion, but the investigation must wait until the tunnel is safe to inspect, officials said.

Milwaukee County District Attorney E. Michael McCann on Friday said he was ordering an inquest into the deaths of the men, who died Thursday."We wanted to have that (inquest) available in case we have to subpoena anyone," McCann said. He said the deaths were "just absolutely tragic."