Detective Chief Inspector Walter Dew (17 April 1863 – 16 December 1947) was a British Metropolitan Police officer who was involved in the hunt for both Jack the Ripper and Dr Crippen.

Dew was born at Far Cotton, in Hardingstone, Northamptonshire, one of seven children to Walter Dew Sr (ca 1822–1884), a railway guard, and his wife Eliza (ca 1832–1914). His family moved to London when he was 10. As a boy Dew was not a natural scholar, and left school aged 13. As a youth Dew found employment in a solicitor's office off Chancery Lane, but not liking the work he became a junior clerk at the offices of a seed-merchant in Holborn. Later, he followed his father on to the railways, for on the 1881 census he is listed as a 17-year-old railway porter living in Hammersmith in London. However, in 1882 he joined the Metropolitan Police, aged 19, and was given the warrant number 66711. He was posted to the Metropolitan Police's X Division (Paddington Green) in June 1882. On 15 November 1886, Dew married Kate Morris in Notting Hill. They had six children, one of whom died in infancy.

Early in 1887, Dew was transferred to Commercial Street police station in H Division (Whitechapel), where he was a detective constable in the Criminal Investigation Department during the Jack the Ripper murders of 1888.

In his memoirs, published fifty years later in 1938, Dew made a number of claims about being personally involved in the Ripper investigation. Dew claimed to know Mary Jane Kelly by sight. "Often I saw her parading along Commercial Street, between Flower and Dean Street and Aldgate, or along Whitechapel Road", he wrote. "She was usually in the company of two or three of her kind, fairly neatly dressed and invariably wearing a clean white apron, but no hat." Dew also claimed to have been one of the first police officers on the murder scene, though none of the records mentioning those people who were present list his involvement.

Dew wrote that he saw Kelly's mutilated body in her room in Miller's Court and that he regarded it as "the most gruesome memory of the whole of my Police career." Dew wrote that Kelly's open eyes were photographed in an attempt to capture an image of her killer, but police doctors involved in the case had already determined that such an effort would be futile. Dew stated that Emma Smith was the first Ripper victim, a view that has often been contested by Ripperologists, and opined that "Someone, somewhere, shared Jack the Ripper's guilty secret."

In 1898 Dew was promoted to Inspector, and was transferred to Scotland Yard. He moved to T Division in Hammersmith in 1900, and in 1903 was promoted to Inspector First Class and moved to E Division, based at Bow Street. In 1906, he became a Chief Inspector, and returned to Scotland Yard. By the time of his retirement from the police in 1910 Dew had received 130 recommendations and rewards from the Commissioner of the Metropolitan Police, judges and magistrates.

In 1898, Dew was involved in bringing international jewel-thief William Johnson, known as 'Harry the Valet', to justice. Johnson stole jewellery then valued at £30,000 from Mary Caroline, Dowager Duchess of Sutherland while she was travelling by train from Paris to London with her husband, Sir Albert Rollit MP, and her brother, his wife and the Duchess's footman and maid. Dew investigated the case together with Inspectors Walter Dinnie and Frank Froest. They tracked Johnson, who by now was spending large amounts of money, to lodgings in London's South Kensington. Despite receiving a seven-year prison sentence, Johnson refused to disclose the whereabouts of the Duchess's jewels, and only £4,000 worth were ever recovered.

Dew had a small role in the Druce-Portland case: he supervised the exhumation of the remains of T. C. Druce in 1907 which effectively put an end to the Druce claims.