Factory Benelux was the place where they occasionaly used to release spare tracks and experimental stuff, wasn't it? Well, "Murder" fitted perfectly the profile of a Benelux release.
As for Les Disques Du Crèpuscule, they were also part of the Belgian connection. I will quote Frank Brinkhuis website as well, that's how everything started.
In October 1979 Michel Duval, a journalist, and Annik Honoré had started organising gigs and events at the Plan K in Brussels. The Plan K, opened in 1973, was a five stories high dismantled sugar refinery, turned into an arts centre, located at 21 Rue de Manchester. Joy Division (gigging abroad for the first time), Cabaret Voltaire and William Burroughs performed at the promoters duo's first night on October the 16th. They were later followed by many hot and important bands from the post-punk era, most of them British. For one reason or another, especially the Factory artists enjoyed their stay in Brussels. Duval's idea to release some (shelved) Factory material was picked up by Factory boss Tony Wilson and Factory Benelux was born, in the Spring of 1980. But since Duval was also interested in releasing material from other artists and bands, he founded his own label: Les Disques Du Crepuscule, in April 1980.
Rue de Manchester, eh? What a coincidence! And we all know why Ian Curtis enjoyed his stay in Brussels. ;)