Divers scouring the toppled Italian cruise ship are working in darkness so complete that they search for bodies by touch.
The description of the laborious search came today from Sara and John Heil, who are at the site awaiting word that the bodies of their parents have been found.
"As the days come and go we find this to be such an extreme test of our patience," they said in a statement released late Wednesday. "We so badly want Mom and Dad to be found so we can bring them home."
Their parents, Jerry and Barbara Heil, are the only Americans still missing from the Jan. 13 crash that partially sank the luxury ocean liner Costa Concordia. Sixteen people have been confirmed dead and another 16 are still missing.
"We continue to monitor first-hand the ongoing search efforts taking place in Italy," the family said. "The conditions in which the divers are forced to operate are undoubtedly making this a very slow process."
The Heil family statement said they have been told that divers are working in an area of the huge ship where they believe they might find the missing bodies. The area is under 60 feet of water, making it a time consuming operation to get to the search area.
The return to the surface is also done slowly to allow the divers time to decompress. Because of the depths, divers are restricted in how frequently they can dive down to the search area.
The most difficult part of the search, however, is the murky conditions in which they are working.
"Due to the depth and the fact that they are inside the ship, they are searching in complete darkness and the visibility is approximately one foot. We can only imagine that much of their searching must be done 'by feel' inside a ship that is over 900-feet long and may have up to 17 floors," they said in their statement.
"The term 'needle in a haystack' certainly seems like an appropriate comparison. We continue to pray for the safety of those searching and express our sincere gratitude for all of their efforts," the family said.
Jerry, 69, and Barbara Heil, 70, were a devoutly religious couple from White Bear Lake, Minn. They had retired fairly recently and the trip to Italy and cruise were considered to be their trip of a lifetime.
The children have prayed in the San Pietro Apostolo Church on the Italian island of Giglio where the ship struck rocks. Family friends have been praying back home in Minnesota for the missing couple.
ABC News' Phoebe Natanson contributed to this report