Jill Dando(PA photos)

"Human society requires co-operation and mutual forbearance," a professor of criminal law once told me.

"And someone who kills sticks two fingers up at that...makes the rest of us shiver."

Six out of ten murders involve people in close relationships with each other. In eight cases out of ten, the killers know their victims.

Murderers standing handcuffed in the dock, always appear to me to be the sort who could be selling insurance or winning the pub quiz. Another thing about murderers that makes us shiver is their sheer ordinariness.

Murder is also extremely difficult to get away with. Buried bodies have a habit of being uncovered by dogs. Corpses thrown into lakes tend to decompose, break up and float to the surface.

Technology enables saliva, snot, semen or sweat to be matched, even years later.

Alibis can be difficult to invent. For a killer, "Where were you on the night of...?" can be the killer question.

Yet occasionally, someone does appear to 'get away with it'. Of all kinds of murder, it is the unsolved ones that make us shiver most of all.

Cornwall-based journalist Brian Pedley has worked in national and local newspapers and TV since 1969. Running his own office for the past 17 years, Brian`s pet subjects are travel, the outdoors - and murder.