From papal speeches to street protests , death penalty news loomed large in 2015.

Some states like Pennsylvania, Nebraska and Connecticut informally halted or outright struck the practice from their books, while others like Texas and Oklahoma scrambled to keep their death chambers running -- sometimes with disastrous results.

A lethal injection procedure became the subject of a U.S. Supreme Court case , prompting one justice to write a dissent that all but invited a constitutional challenge to the practice.

Six people were exonerated from death rows around the nation, while the rate of executions overall dropped to its lowest level in almost two decades.

The fewest number of people were sentenced to death in 2015 than in any year since the Supreme Court declared many state death penalty systems "cruel and unusual" and capital punishment across America was halted from 1972 to 1976.

"2015 has been a historic year in a number of respects," said Robert Dunham, executive director of the Death Penalty Information Center , who wrote a year-end report on capital punishment released Wednesday.

Read the full report.

A total of 28 executions were carried out this year in just six states -- the fewest number of executions since 1991, Dunham notes in his report. Just 49 death sentences were handed down, a 33 percent drop from last year.

Even states like Texas, Missouri and Georgia, which were responsible for most of the executions this year, offer proof that the death penalty is in decline. "The people they executed [this year] were sentenced to death in '80s and '90s," Dunham told The Huffington Post.

"Montana, Virginia and Georgia did not sentence anyone to death this year," he added, "and Texas only sentenced three people to death."

Because of changes to some state laws, more defendants are receiving competent taxpayer-funded lawyers and, unlike in the past, jurors are being told that their sentencing options include life without parole.

In the 1980s and 1990s, Dunham said, "procedural safeguards were weaker" for death penalty defendants, and "U.S. hysteria about crime" was at a peak.

"These are the cases that are coming up for execution now," he said. "And they're fraught with legal error, with bias, and are generally regarded as the least reliable convictions in death sentences that have been imposed."