unaccounted for~

砂州に乗り上げて転覆したイタリアの客船は現代のタイタニック事故と揶揄されています。account forの反意の表現、unaccounted for~はどのような意味でしょうか。Lbow-Shoulderくん、どうぞ。（GP）
Porto Santo Stefano, Italy (CNN) -- Rescuers reached two trapped honeymooners in the interior of a cruise ship more than 24 hours after it ran aground off a picturesque Italian island, killing three people, injuring 20 and leaving dozens unaccounted for. The South Korean passengers, each 29, heard searchers calling out on the Costa Concordia, Italy's ANSA news agency reported early Sunday. They were located in a cabin and taken ashore. Video showed them being taken to a waiting ambulance.

The captain of the ill-fated vessel, which turned over on its side after the grounding, was arrested late Saturday and was being investigated for abandoning ship and manslaughter, a local prosecutor said. With perhaps up to 50 people unaccounted for, divers suspended their efforts at dark, with plans to resume the search in the azure waters off the island of Giglio at dawn Sunday. Accounts of the chaos from many of the 3,200 passengers were reminiscent of a maritime disaster 100 years ago this April -- the loss of the RMS Titanic.
"For me, the worst part of the whole ordeal" was when a lifeboat crew member told those boarding that it was "women and children first," said passenger Benji Smith of Boston.
"All these families who were clinging to each other had to be separated," Smith told CNN. Some passengers fell into the chilly waters during the rescue, ANSA reported.
Questions abounded: Why was the colossal ship so close to the shore? How fast was it moving? How well did the crew respond? According to many passengers, the evacuation was disorganized and no one seemed in charge.
"Every crew member who walked past shouted instructions, but the instructions contradicted each other," Smith said.
Concordia's captain, Francesco Schettino, was interviewed earlier Saturday about what happened when the ship struck rocks in shallow water off Italy's western coast Friday evening, said officer Emilio Del Santo of the Coastal Authorities of Livorno. Local fishermen say the island coast of Giglio is known for its rocky sea floor.
Schettino said "that rock was not indicated on the chart," according to ANSA. "Me and the crew, we were the last to abandon ship," he said.
The ship was 2.5 miles off route when it struck the rocky sandbar.

http://edition.cnn.com/2012/01/14/world/europe/italy-cruise-deaths/index.html?hpt=hp_t1