The US also has a lot more deprivation than here, which is linked fairly directly to crime. Yes, we would have to pay for someone in prison for life, but keeping someone in prison for life in a 12x10 foot cell with no TV or anything like that, locked up for 22 hours a day (as they do in US maximum security jails), is a little cheaper than people like Ian Huntley being watched by his own dedicated team 24 hours a day, having the full Sky package in his cell, a double bed and all thie rest of it I'd imagine.
And very few murders are planned, hence destroying the evidence doesn't really come into many peoples heads, at least in any significant way. I'd wager most of the unsolved, so called cold case murders in this country are the ones that were properly planned.
So you advocated one of the lads who killed that poor girl up in Bolton purely because she was dressed as a goth having his sentence reduced by 6 months last week do you, since that will save the taxpayer some money?