Why are some prison sentences so long?

After sentencing, the judge told Ariel Castro he was too dangerous to ever be released

Kidnapper and rapist Ariel Castro has been sentenced to life without parole plus 1,000 years. What's the point in extending a prison term beyond a person's lifetime, asks Tom Geoghegan.

Sentencing is not just about determining how long someone should be behind bars, it also has a symbolic, theatrical function, says Franklin Zimring, a professor of law at the University of California, who has written extensively about deterrents.

"In sentencing Bernie Madoff [to 150 years for fraud], what the judge wants to be telling him is 'you are really a bad person.' And for this purpose, the number of years can be endlessly elastic."

How much symbolic denunciation plays a part can depend on many things, such as media coverage or the nature of an offence, but the tension between these two radically different functions - the symbolic and practical - is a feature of modern criminal justice systems, he says, and not just in the US. There was a famous case in Spain where a fraudster received a 2,000-year sentence.

Parole means the sentence can be adjusted at a later date. But it has been eliminated for life sentences in many parts of the country.

Most criminal prosecutions in the US are brought by the state, so there can be huge variations in sentencing. Judges are constrained by a statutory range but, depending on the crime, that could be very broad or have no maximum sentence at all.

Fraud against one person can involve multiple crimes like false statements, wire fraud and theft, so consecutive sentences for each charge can fast add up. The same goes for crimes involving a computer, like child pornography, because each image could be a separate count. Minor misdemeanours are more likely to result in concurrent sentences.

For victims of crime and their loved ones there is nothing problematic about a very long sentence. Indeed, a sentence that increases with each guilty charge is a way of telling each victim that they matter.

Some long sentences are an alternative to the death penalty. Dudley Wayne Kyzer is serving two life terms plus 10,000 years for a triple murder he committed in the 1970s. After four years on death row, he was given a second trial because the death penalty in Alabama was at the time deemed unconstitutional.

Tommy Smith was Tuscaloosa County Assistant District Attorney when he persuaded the trial judge to impose the long sentence as an alternative. "The jury sent a message. They don't want him released," he said. Kyzer has been denied parole nine times.