Examples:
"... injuries were so severe they were incompatible with life." = Their injuries were so severe that the patient died.
"... is assisting Police with their enquiries." = ...is a suspect and is being questioned by Police.
"Child sex offender" = Paedophile
The first one is just plain silly, but I never anyone say it that way?
The third example is not exactly synonymous. One can be charged with offences of that nature without being a paedophile.
edit: grammar fix
I think that's one of those where peculiar patterns of "official speech" than just develops and then gets copied over time.
The classic style once (and possibly still) used by the British police is "I was undertaking my duties while proceeding along Veryordinary Road when I observed the suspect who is now know to me as Mr Jones" instead of saying "I was walking along Veryordinary Road and I saw Mr. Jones".
I think it happened with the British police because they have traditionally been ordinary working class people who found themselves thrust into the very formal and highly educated courts system and they felt they were letting the side down if they spoke plain "rough" English when everybody else sounded so posh. Basically they were doing a serious job, wanted to be taken seriously, so copied the speech patterns, as they saw them, of their "betters" who were also doing the job. The Superintendent would copy the lawyers, the Inspector would copy the Superintendent, the Sergeant would copy the Inspector and the Constables would copy the Sergeant, everything changing a little at each step in that game of Chinese whispers until it developed into the style that it did.
As far as "assisting Police with their enquiries" is concerned: I was sitting in an interview room in an East London police station giving a statement as a witness, when a policeman came in and wanted to discuss something with the policeman who was interviewing me. He obviously wanted to talk about something that he didn't want to discuss in front of a suspect. The copper who was interviewing me said to him "It's OK, this gentleman is just helping us with our inquiries." So, the British police at least, do use that formulation to mean literally "helping" as well as "We don't have enough on him to nick him yet".