Traces of cocaine have been found on a hair sample taken from the captain of the Costa Concordia, according to lawyers representing survivors of the stricken cruise ship.
But the consultant who did the analysis for prosecutors found no presence of the drug in Captain Francesco Schettino's urine or within the strands of his hair, which would have indicated he had used the drug.
Schettino, 52, is under house arrest in his home near Naples while he is investigated for alleged manslaughter and abandoning his ship , which hit a reef off the coast of Italy on January 13.
Thirty-two people are believed to have died, including 15 whose bodies have not been found.
Italian consumer protection group Codacons, which is representing some survivors of the shipwrecked liner, said the DNA samples were taken on January 17.
In a statement, Codacons said the results were "very strange".
It has asked prosecutors investigating Schettino to order another test to see if the samples might have been contaminated, accidentally mislabelled or switched.
Neither prosecutors nor Schettino's lawyer could be reached for comment.
Under Italian law, those attaching civil suits to a criminal case must be informed of, and allowed to monitor, evidence and other developments in the investigation.
The Concordia continues to lie on its side close to the port of Giglio.
It was carrying about 4,200 passengers and crew on a week's cruise when it rammed into the reef during dinner a couple of hours after leaving an Italian port.
The boat started badly listing to one side almost immediately, causing passengers to panic and try to scramble aboard lifeboats.
But the evacuation was not ordered until about an hour later, and some passengers jumped overboard when several of the lifeboats could not be deployed because of the ship's tilt.
Divers are continuing to search sections of the wreckage where some of the missing were last seen in hopes that more bodies can be recovered.
And pumping operations are continuing to remove some 500,000 gallons of fuel from the ship's tanks.
