He was born Donald Nappey in Bradford on August 1, 1936, and changed his name because his daughter was mocked for it. He served in Kenya and Aden with the King's Own Yorkshire Light Infantry, ran a failing joinery business, and drilled himself in a private version of military discipline, building his own weapons store and rehearsing operations in detail.
From 1971 he raided sub-post offices at night, in a black hood, and shot three men: Donald Skepper at Harrogate in February 1974, Derek Astin at Higher Baxenden in September, and Sidney Grayland at Langley in November. The press called him the Black Panther and the raids became a national story.
On January 14, 1975, he took Lesley Whittle, a seventeen-year-old whose family owned a coach firm in Shropshire and whose inheritance had been reported in the local paper, from her bed at Highley. He left a ransom demand punched into strips of Dymo tape and hid her in a drainage shaft in Bathpool Park at Kidsgrove, sixty feet down, tethered by a wire noose. Two ransom attempts failed in a series of police errors that became notorious, including a security man, Gerald Smith, whom Neilson shot and who died a year later. Lesley Whittle was found dead in the shaft on March 7, hanging from the tether.
He was caught by chance on December 11, 1975. Two constables in Mansfield Woodhouse stopped a man loitering by a post office; he pulled a shotgun on them, and they and several passers-by wrestled him into a car and disarmed him.
He was convicted at Oxford in July 1976 of four murders and given five life sentences, with a whole-life tariff confirmed in 2008. He died at Norwich prison on December 18, 2011.