Cruel and Unusual Punishment

From CBS:
Report: '93 World Trade Center bomber sues to end solitary confinement

The article didn't say anything about how the solitary confinement was being challenged, but I'd assume that the challenge is being done with the 8th amendment to the US Constitution:

"Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted."

The only bit we're interested in is the last part - cruel and unusual punishment. That phrase is open to lots of interpretation and argument. There are many different opinions on just what constitutes "cruel and unusual punishment" - in fact, the case which produced the first relevant Supreme Court ruling (Furman v. Georgia) so divided the SCOTUS that each justice wrote their own separate concurrence or dissent. Other cases, including some in recent years have continued to divide the SCOTUS. I'm going to add to the pile of opinions.

A cruel punishment is one that exceeds the crime in terms of severity or goes out of its way to be inhumane. Giving a life sentence to a petty thief would be cruel, as would applying crucifixion or impalement to any offense, even in cases where the offender tortured his victims to death. But the simple death penalty for occurrences of first degree murder is not cruel, nor is life in prison for any malicious act that results in the death of another. The punishment must be appropriate to the crime with sentences increasing in severity based upon the severity of the crime, and with those crimes where physical harm was committed or threatened automatically incurring a higher penalty than any crime where only financial harm was committed.
Unusual is when the punishment is only applied to a few of those who commit crimes of the same type and scale. If most convicted of one specific crime (auto theft, for example) got one sentence, but a select few convicts got a different punishment, that punishment would be unusual - no matter if it was more or less severe that the usual punishment.
Punishment must fit the crime, and the punishment must be applied the same to all convicted of crimes of the same type and severity (thus allowing for different punishments for different amounts of damage done).
This brings me to the death penalty. Many assert that the death penalty is cruel and unusual. While it is almost certainly unusual - most courts hesitate to apply an irreversible penalty, no matter the crime - is is not cruel when applied to those who commit first degree murder (premeditated). Still, due to its irreversible nature, in any case where there is any doubt as to the guilt of the convicted, other means of punishment should be applied, so that if new evidence is found demonstrating the innocence of the accused, they can be exonerated and released. However, in cases where, due to committing the crime in front of cameras/witnesses, taking of souvenirs (a la Ed Gein or Jeffrey Dahmer), confession, or other evidence that leaves no doubt as to the identity of the killer. When someone's life is on the line, there must be no doubt, no chance that someone else committed the crime, so that no one innocent of premeditated murder is executed.