Sir Leonard Wilfred James Costello (25 August 1881 – 2 December 1972) was an English barrister, college lecturer, soldier and colonial judge who was also a Liberal Party politician.
Leonard Costello was born in London, the son of James and Alice Costello. He was educated at Dulwich College and was later president of the Alleyn Club, established in honour of the school's founder. He then went to Peterhouse College, Cambridge where he gained BA and LL.B degrees in 1902 and an MA in 1906. In 1907 he married Winifred Avery, the daughter of Thomas Belgrave and they had two daughters. His first wife died in 1950 and in 1952 he married Joan Piper, the daughter of George Hewitt. She died in 1972.
Costello was called to the Bar at the Inner Temple in 1903. He then practised on the Midland Circuit from 1903 to 1926. Between 1906 and 1908 he had a position as a lecturer in law at University College, Nottingham. He later went out to India where, from 1926–1940, he was a judge in the High Court in Calcutta. He was Acting Chief Justice of Bengal in 1937 and again 1939. In 1937, he was strongly criticised by the Indian National Congress after remarks he made in a murder trial that the poor education and biased approach of potential jurors made the jury system unsuitable in India. It was widely believed that the jury in the case had made up their mind to find the defendant guilty despite what Costello regarded as conclusive evidence of guilt. Costello was nevertheless knighted in 1935 for his role as a Bengal judge and was awarded the CBE in 1946.
The Bhawal case ran from 1933 to 1946, creating a sensation across India, with courts involved in London, Calcutta and Dhaka. In a case with echoes of the famous Tichborne Claimant, the court action was concerned with the dispute of inheritance of an estate and the identity of the Second Kumar of Bhawal (a Bengali princeling or zamindar) who was declared dead under mysterious circumstances, and who came back to life after twelve years.