"Des" was the nickname that was part of Nilsen's public persona. Luke Neal told Radio Times: "'Des' was something that Dennis Nilsen called himself. To people that knew him, Nilsen was head of a union. He was somebody who was a champion of the downtrodden. He was somebody who was nice to people. But 'Des' was a construct that Dennis Nilsen had made in order to get people back to his flat and to kill them."
The script is based on the book "Killing for Company" by Brian Masters, who interviewed Nilsen while he was in prison.
Nilsen's youngest victim was only 14 years old.
Dennis Nilsen was 37 years old at the time of the events depicted. David Tennant was 48 at the time of filming.
David Tennant's casting and uncanny physical resemblance to serial killer Nilsen was praised by many commentators. The role was a significant contrast to earlier perceptions of Tennant, who was considered more of a sex symbol in previous roles such as the doctor in Doctor Who (2005).