Michael Campbell, assistant professor of criminal justice at the University of Missouri-St. Louis, said some lawmakers simply don't believe convicted murderers deserve any mercy.
"Many of these politicians are trying to tap into a more populist theme that those who do terrible things deserve to have terrible things happen to them," Campbell said.
Richard Dieter, executive director of the Death Penalty Information Center in Washington, D.C., cautioned that there could be a backlash.
"These ideas would jeopardize the death penalty because, I think, the public reaction would be revulsion, at least from many quarters," Dieter said.
Some states already provide alternatives to lethal injection. Condemned prisoners may choose the electric chair in eight states: Alabama, Arkansas, Florida, Kentucky, Oklahoma, South Carolina, Tennessee and Virginia. An inmate named Robert Gleason Jr. was the most recent to die by electrocution, in Virginia in January 2013.
Missouri and Wyoming allow for gas-chamber executions, and Arizona does if the crime occurred before Nov. 23, 1992, and the inmate chooses that option instead of lethal injection. Missouri no longer has a gas chamber, but Attorney General Chris Koster, a Democrat, and Missouri state Sen. Kurt Schaefer, a Republican, last year suggested possibility rebuilding one. So far, there is no bill to do so.
Delaware, New Hampshire and Washington state still allow inmates to choose hanging. The last hanging in the U.S. was Billy Bailey in Delaware in 1996. Two prisoners in Washington state have chosen to be hanged since the 1990s — Westley Allan Dodd in 1993 and Charles Rodman Campbell in 1994.
Firing squads typically consisting of five sharpshooters with rifles, one of which is loaded with a blank so the shooters do not know for sure who fired the fatal bullet. They have been used mostly for military executions.
In recent years, there have been three civilian firing squad executions in the U.S., all in Utah. Gary Gilmore uttered his famous final words, "Let's do it," on Jan. 17, 1977, before his execution, which ended a 10-year moratorium on the death penalty.
Convicted killers John Albert Taylor in 1996 and Ronnie Lee Gardner in 2010 were also put to death by firing squad.
Utah is phasing out its use, but the firing squad remains an option there for inmates sentenced prior to May 3, 2004.
Oklahoma maintains the firing squad as an option, but only if lethal injection and electrocution are deemed unconstitutional.
In Wyoming, Republican state Sen. Bruce Burns said death by firing squad would be far less expensive than building a gas chamber. Wyoming has only one inmate on death row, 68-year-old convicted killer Dale Wayne Eaton. The state has not executed anyone in 22 years.
Jackson Miller, a Republican in the Virginia House of Delegates, is sponsoring a bill that would allow for electrocution if lethal injection drugs are not available.
Miller said he would prefer that the state have easy access to the drugs needed for lethal injections. "But I also believe that the process of the justice system needs to be fulfilled."