The trials in Singapore of Japanese soldiers on charges of war crimes began in January 1946. In the first trial, CaptainGozawa Sadaichi and nine other Japanese soldiers were accused of maltreating Indian prisoners of war who refused to join the Japanese-sponsored Indian National Army. The British were conscious of the need for a fair trial to avoid accusations of "victor's justice", to bolster the argument for preserving the British Empire. Accordingly, the defendants were granted full legal representation, and Sleeman acted as senior counsel for the defence. Sleeman's efforts on behalf of the defendants were praised by the tribunal. One defendant was acquitted; eight were sentenced to terms of imprisonment, Sadaichi to 12 years, and the others to lesser terms; and Lieutenant Kaniyuki Nakamura was sentenced to death for the illegal execution by beheading of an Indian serviceman accused of planning to escape. Sleeman also acted for the defence in a second trial in Singapore, which took place in March and April 1946. In the "Double Tenth" trial, 21 members of the Kempeitai were accused of war crimes relating to the torture of 57 of prisoners following a raid on Changi Prison on 10 October 1943 to investigate of a suspected spy network, thought to be responsible for the sinking of seven Japanese merchant vessels in Singapore harbour in September 1943. Many were brutally tortured; one prisoner was executed; another attempted suicide, was refused medical attention, and was left to die of his wounds; and several others died afterwards. The commanding officer, Lieutenant Colonel Sumida Haruzo and seven others were sentenced to death, three to life imprisonment, and others to shorter terms of imprisonment. Sleeman published an account of the trial of Gozawa Sadaichi in 1948, with a foreword by Earl Mountbatten of Burma. With Sam Silkin, he published The Double Tenth Trial, an account of the trial of Sumida Haruzo in 1951, with a foreword by Viscount Simon.
Legal career
After he left the army, Sleeman returned to the bar, practising mostly in the divorce courts. He was junior counsel for the defence in the trial of John Christie, accused of murdering his wife Ethel at 10 Rillington Place. He was appointed as a recorder in 1975 and then as a circuit judge in 1976, serving in that position until 1986, initially in Coventry and later in Surrey.