Only five of the 28 people who disappeared from cruise ships in the past three years were found, according to data disclosed to Congress by the world's largest cruise lines.

A congressional memo compiled in advance of a House hearing on cruise ship safety Tuesday also details 177 sexual misconduct incidents, ranging from inappropriate touching to rape, and four robberies of amounts over $5,000.

During that three-year period approximately 25 million people embarked on cruises from North America ports, the memo said.

Disclosure of the data, supplied by Holland America Lines, Royal Caribbean Cruises and others, is unusual because cruise lines are not required by law to publish comprehensive crime statistics and criminal law varies greatly on international waters.

Rep. Christopher Shays, R-Conn., wants to change that.

"I don't have a comfort level that statistics from the cruise industry are accurate," he said Saturday in a telephone interview. "I've never known statistics that are voluntary to be accurate."

Shays, chairman of the House Subcommittee on National Security, is working on legislation to make such reporting mandatory.

FBI Assistant Director Chris Swecker testified before Shays' panel in December that the FBI opened 305 crime cases on the high seas since 2001.

"We know all crimes (aboard cruise ships) aren't being reported, so I think a requirement that (cruise lines) report crimes either to the FBI or to the Coast Guard or both would be a start," said Swecker.

Shays said he found it "unsettling" how quick the industry was to push back at his efforts on reporting requirements. "I had to tell the cruise industry that last thing to get us off this issue is pressure to get off this issue," he said. "It makes me suspect there is something there that they don't want to know about."

He added: "I think the fact they don't want us to know how many security people they have is kind of curious."

James Fox, a professor of criminal justice at Northeastern University retained by the International Council of Cruise Lines, said in a statement issued by the council that, "While virtually no place — on land or sea — is totally free of risk, the number of reported incidents of serious crime from cruise lines is extremely low, no matter what benchmark or standard is used."

"The cruise lines cooperated with Congress in gathering these statistics to further demonstrate that cruising is an exceptionally safe vacation," Michael Crye, president of the industry group, said in the statement. He said 15 cruise lines submitted data for the report.

The subcommittee hearings come amid the highly publicized disappearance of a constituent from his honeymoon cruise last summer.

In July 2005, George Allen Smith IV and his wife, Jennifer Hagel-Smith, were aboard the Royal Caribbean Line's Brilliance of the Seas while as it sailed from Turkey to Greece in the Mediterranean Sea.

Smith, a 26-year-old lawyer from Greenwich, Conn., disappeared after an apparent late night of drinking. Blood stains were found on the railing of his cabin, but no body was ever found.

The FBI is investigating, and no one has been charged. Smith's family has accused Royal Caribbean of covering up the disappearance, an assertion the company denies.