As the penalty phase begins Tuesday for Boston Marathon bomber Dzhokhar Tsarnaev, who cast himself as an avenger of crimes against Muslims, it might be interesting to consider what Islamic law says about capital punishment.

Like U.S. federal law, under which Tsarnaev was convicted, Islamic law permits capital punishment for severe crimes such as murder or treason. Where Islam differs markedly is that victims, including relatives of the dead, may actually be allowed to decide whether the convicted person receives life or death.

Although U.S. law allows victim impact statements to be considered in sentencing, victims don't get to argue in court for or against the death penalty. Of course a number have already expressed their opinions elsewhere.

Most compellingly, Bill and Denise Richard, whose 8-year-old son was murdered and 7-year-old daughter lost a leg, told the Boston Globe that they favor life without parole, as long as Tsarnaev waives any right to appeal. But the court alone will decide Tsarnaev's fate, and I'm grateful for that.

If victims got to decide, it would open the door for both forgiveness and revenge, and be a huge responsibility in their emotional state. Besides, with so many victims in this case, whose hurt would prevail?

Ingrid Mattson, former president of the Islamic Association of North America, spoke with me about the death penalty when I interviewed her for a 2013 Commonweal profile, and while she didn't convince me to embrace the Islamic view, I did gain a certain appreciation for it.

In Islam, she said, "It is allowed to retaliate, but it is better to forgive.” And although forgiveness in Islam is the highest spiritual state, there's no shame for those who can’t bring themselves to embrace it.

Mattson insisted the Islamic system isn't arbitrary; rather it "takes into account that people are different, and that it (crime) is always personal.” She cited, as an example, the horrific 2007 incident in which two men invaded the Cheshire, CT home of Dr. William A. Petit Jr., beat him unconscious, then tortured and murdered his wife and two young daughters.

Petit, a Catholic, wanted the killers sentenced to death. He got his wish, although it could be decades, if ever, before the sentence is carried out, especially since in 2012 Connecticut abolished the death penalty (joining Massachusetts) for subsequent capital crimes. Alas, Petit has not heard the last of his family's murderers.

In cases like this, said Mattson, the family “should have a say, because they have suffered the most. In some sense they’ll never feel like they’ve done enough (to achieve justice) unless this person (murderer) has been killed."

The Cheshire murders “affected society, too,” said Mattson, “but how much did it affect me compared to Dr. Petit?" He thinks about it every day, she said, while she thinks about it when it’s remembered in the newspapers.

Those who lost loved ones or were maimed in the Boston bombing think about it every day, as do many who helped the wounded, narrowly escaped the carnage, or were simply there. I think about it whenever it's in the news again. 

Mattson said that while forgiveness is best, "There’s not a real value judgment in Islamic law if you can’t arrive at a state of forgiveness. You have the right to insist on capital punishment, because some people just can’t get beyond it, can’t feel safe, even if the person is in jail.”

Bill and Denise Richard have said nothing about forgiveness, only that they want life for Tsarnaev to spare their family death sentence appeals. But the Cheshire case presents a cautionary tale. When one of those killers tried to waive his right to appeal, his lawyer claimed he was mentally unfit to do so.

The Boston Marathon bombing traumatized an entire city, even the country, similar to the 1995 bombing of a federal building in Oklahoma City by Timothy McVeigh. Some victims preferred a life sentence for McVeigh, just as some prefer it for Tsarvaev. But the state decided that McVeigh had to die.

Similarly, Islam allows the state to execute someone even over the wishes of victims' families if it decides that the killer, or traitor, is a threat to society that can’t be eliminated any other way.

If Tsarnaev is sentenced to death, he will cast himself as a martyr. Some argue that if he is allowed to live, he could radicalize others from prison, although it seems to me the state ought to be able to prevent that.

Bottom line: it's impossible to know if Tsarnaev is more of a threat alive or dead. And, in our sorrow and anger, it's hard to think about the penalty phase in any other terms. But he is 21 years old. 

If sentenced to life, sometime during the decades ahead he might learn what Islam actually teaches about harming the innocent. He may never get forgiveness, but should he seek it, wouldn’t that mean something?