One abiding principle of the justice system goes: The punishment should fit the crime and the defendant. That helps explain the thinking behind reserving the death penalty for the worst of the worst. It also puts in context legislation at the Statehouse that would prohibit the execution of those who are convicted of murder and suffered from a serious mental illness at the time of the crime.

The idea isn’t to absolve people of responsibility for their actions. Rather, as Terry Russell, the executive director of the National Alliance on Mental Illness of Ohio, recently told the Columbus Dispatch, “ … people with these mental illnesses don’t always know what they’re doing.” He added: “We don’t think it’s ethically or morally right to take their life. ... ”

The legislation is framed narrowly. To qualify, a person must be diagnosed with one of five mental illnesses, schizophrenia, schizoaffective disorder, bipolar disorder, major depressive disorder or delusional disorder. More, at the time of the killing, the illness must have “significantly impaired the person’s capacity to exercise rational judgment.” So this isn’t something easily gamed by attorneys and defendants.

Neither does the bill amount to duplication. Some critics argue the option of entering a plea of “not guilty by reason of insanity” already protects those with severe mental illness from execution. Yet, as proponents note, the conditions identified in the legislation would not qualify for such a plea.

In that way, the legislation fills a troubling gap, or as state Rep. Brett Hudson Hillyer, a Uhrichsville Republican and the primary sponsor of the bill, reasoned at a legislative hearing last month: “ … most will concede that executing an individual found to be suffering from a serious mental illness at the time of the crime is neither just nor fair.” He stressed the death penalty should apply to those who have acted “intentionally.”

Another concern of critics is that with enactment, prisoners currently on death row would overwhelm the courts with requests to reconsider their sentences. That may be so, though it represents a necessary short-term price for getting right capital punishment. It is also worth noting that mental health organizations have assessed the population of death row and project that 5 percent to 10 percent of prisoners would meet the required threshold.

The few granted such a reprieve hardly would escape severe punishment. Their death sentences would shift to life in prison without the possibility of parole, or perhaps some would become eligible for parole in 25 years or 30 years. Under the proposed law, those facing murder charges would have the option of citing a serious mental illness. The court would make an evaluation. If the judge found for the defendant, the trial would proceed without the death penalty.

That would represent an improvement. As things stand, in the second phase of a capital trial, the jury weighs whether to apply the death penalty. Research shows that many jurors see mental illness as an aggravating factor, its presence making a death sentence more likely. This goes to the familiar and persistent prejudice toward mental illness.

Consider the supporters of the legislation, including the Ohio Psychological Association and the Ohio Psychiatric Physicians Association. A task force that looked at ways to improve the death penalty recommended by a 15-2 vote that the state prohibit the execution of those with a serious mental illness. As far back as 2006, the American Bar Association took the same stance. The thinking is that the death penalty involves more than the killer. Its conduct reflects something larger — our shared obligation to see that the punishment fits the crime and the defendant.