Thirty-two states authorize capital punishment, but it is becoming increasingly difficult to carry out because of a shortage of the drugs used in lethal injections, the primary method used. States have been trying new combinations of different drugs, and executions haven't always gone smoothly with the new protocols.
Numerous legal challenges have been launched, and some executions have been botched, leading some states to review their methods and to seek alternatives. Other states simply aren't carrying out capital punishment because their governors are opposed to it.
Here is a look at what's happening with some of the states that have the death penalty on the books.
Arizona, Ohio, Oklahoma
These three states have put executions on hold because of botched executions last year. It took Joseph Wood nearly two hours to die in Arizona. In Ohio, Dennis McGuire gasped and snorted for an extended period before dying. Clayton Lockett in Oklahoma had a heart attack soon after being injected.
Calling it a "flawed system," Gov. Tom Wolf made Pennsylvania the most recent state to impose a moratorium in February. It will remain in effect pending the results of a task force that is reviewing the punishment. Pennsylvania has one of the largest death row populations in the country — 188 people — but has carried out only three executions since 1976.
Gov. John Kitzhaber imposed a moratorium in November 2011 saying he wanted no part of the "inequitable" system and vowing that no executions would be carried out as long as he is in office. An inmate was scheduled to die within weeks of that decision. Thirty-seven people are on death row.
Gov. Jay Inslee imposed a moratorium in February 2014, affecting nine people on death row. State legislators opposed to the death penalty introduced a bill in January seeking to abolish it. They have tried and failed before, but are hoping the governor's personal moratorium will help build support this time. Washington is the only state where inmates are offered the choice of death by hanging instead of lethal injection, the default method. No one has been executed since 2010.
The state has rarely used the death penalty and hadn't executed anyone since 1997 before Gov. John Hickenlooper imposed a moratorium in 2013. He said that if the death penalty is to be carried out it should be done so "flawlessly," but the system is not flawless. Three inmates are on death row.
Legislators opposed to the death penalty introduced a bill earlier this month to repeal it. If it passes, Delaware would be the 19th state to ban it, but the 15 people currently on death row could still be executed. Opponents have tried and failed before to overturn the death penalty in Delaware.
Florida's death penalty will be on trial at the U.S. Supreme Court this session. It agreed to hear a case about how juries recommend death sentences and whether the rules are constitutional. In Florida, juries do not have to be unanimous in their recommendation.
The state has the country's largest death row population, more than 700 people, but the state imposed a moratorium in 2006 after a successful court challenge that forced the state to change its lethal injection protocols. New regulations were introduced in 2010. Last summer a federal judge in the state declared the death penalty unconstitutional, but the ruling only applied to a single case.
In 2014, Gov. Bill Haslam signed a law that authorizes the use of the electric chair if lethal injection drugs are not available. Some states give death row inmates the option of the electric chair, but Tennessee's law now makes its use mandatory if drugs can't be used.
Kansas, Nebraska, Nevada, New Hampshire, Wyoming
There are no formal moratoriums, but these states have not carried out an execution in more than five years. Kansas, for example, hasn't imposed the sentence since 1965. New Hampshire hasn't executed anyone since 1939. It has one person on death row. The legislature came one vote short of abolishing the death sentence last year.
Arkansas, Kentucky, Louisiana, Montana, North Carolina
These states have put executions on hold pending court challenges over the drugs being used in lethal injections.
Missouri’s oldest death row inmate Cecil Clayton was executed on March 17. The 74-year-old convicted murderer had an IQ of 71, according to his lawyers, who argued that he should have been ineligible for the punishment because he wasn’t mentally healthy. The part of the brain that controls impulse and judgment had been removed from Clayton after a sawmill accident. The last-minute appeals all failed.
States with the death penalty
Alabama, Arizona, Arkansas, California, Colorado, Delaware, Florida, Georgia, Idaho, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, North Carolina, Ohio, Oklahoma,
Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Washington, Wyoming.
States without the death penalty
Alaska, Connecticut, Hawaii, Illinois, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, New Mexico, New York, North Dakota, Rhode Island, Vermont, West Virginia, Wisconsin.