It could be one of the nation’s oldest cold case files: What happened to eight Confederate sailors aboard the CSS H.L. Hunley after it became the first submarine in history to sink an enemy warship?

Their hand-cranked sub rammed a spar with black powder into the blockade ship USS Housatonic off Charleston on a chilly winter night in 1864 then disappeared.

The Hunley’s fate has been the subject of almost 150 years of conjecture and almost a decade of scientific research since it was raised in 2000. But the submarine has been agonizingly slow surrendering her secrets.

Scientists hope the next phase of the conservation, removing the hardened sediment coating the outside of the hull, will provide clues to the mystery.

McConnell, who watched the sub being raised more than eight years ago, thought at the time the mystery would easily be solved.

But what seemed so clear then seems as murky now as the sandy bottom where the Hunley rested for 136 years. When the Hunley was raised, the design was different from what scientists expected and there were only eight, not nine, crewmen, as originally thought.

The first phase of work on the Hunley consisted of photographing and studying the outside of the hull. Then several iron hull plates were removed allowing scientists to enter the crew compartment to remove sediment, human remains and a cache of artifacts.

Archaeologist Maria Jacobsen said the Hunley is like a crime scene except that, unlike on television shows, there is no smoking gun.

In the case of the Hunley, some of those fingerprints may be covered with the encrusted sediment on the hull that scientists refer to as concretion.

When the sub was found, there was no window in the front conning tower, suggesting it had been shot out, perhaps by Union sharpshooters.

But no glass was found inside the sub and the remains of the captain, Lt. George Dixon, showed no injuries to his skull or body consistent with being shot while looking through the window, McConnell said.

The crewmen’s bodies were found at their duty stations, suggesting there was no emergency resulting in a scramble to get out of the sub. The controls on the bilge pump also were not set to pump water from the crew compartment, suggesting there was no water flooding in.

After the attack, Confederates on shore and Union ships reported seeing a blue light, believed to be the Hunley signaling it had completed its mission.

But after the attack, the USS Canandaigua rushed to the aide of the Housatonic and there is speculation that the light could have come from that ship instead.

Then there is the mystery of Dixon’s watch, which stopped at 8:23 p.m. Although times were far from uniform in the Civil War era, the Housatonic was attacked about 20 minutes later, according to federal time, McConnell said.