In December 1943, following official protests, the Japanese government issued a statement formally denying responsibility for the sinking of Centaur. Records provided by the Japanese following the war also did not acknowledge responsibility. Although Centaur's sinking was a war crime, nobody was tried for sinking the hospital ship. Investigations into the attack were conducted between 1944 and 1948, and included the interrogation of the commanders of the submarines operating in Australian waters at the time, their superiors, plus junior officers and crewmen from the submarines who had survived the war. Although several of the investigators suspected that Nakagawa and I-177 were most likely responsible, they were unable to establish this beyond reasonable doubt, and the Centaur case file was closed on 14 December 1948 without any charges laid.
Historians were divided on which submarine was responsible. In Royal Australian Navy, 1942–1945, published in 1968 as part of the series detailing the Australian official history of World War II, George Hermon Gill concluded that either I-178 or I-180 was responsible; the former was more likely as she had served in Australian waters the longest of any Japanese submarine at the time, but had claimed no kills in the three-month period surrounding Centaur's sinking. However, in 1972, German military historian Jürgen Rohwer claimed in Chronology of the war at sea that I-177 torpedoed Centaur, based on a Japanese report stating that I-177 had attacked a ship on 14 May 1943 in the area the hospital ship had sunk. Japanese Rear Admiral Kaneyoshi Sakamoto, who had shown Rohwer the report, stated that Nakagawa and I-177 were responsible for the attack on Centaur in his 1979 book History of Submarine Warfare.
As an official history of the Japanese Navy, Sakamoto's work was considered to be official admission of the attacking submarine's identity. Subsequently, most sources assumed as fact Nakagawa's and I-177's role in the loss of Centaur. Nakagawa refused to speak on the subject of the attack on Centaur following the war crimes investigation at the end of World War II, even to defend himself or deny the claims made by Rohwer's and Sakamoto's works, and died in 1991.