WASHINGTON - Expect another long day of legal wrangling Thursday over Arkansas' plan to execute inmates in the coming week.

Ledell Lee and Stacey Johnson were to be put to death Thursday night, but Johnson's execution was at least temporarily halted and Arkansas' ability to use one of its execution drugs was called into question. Lawyers for inmates filed multiple legal challenges to derail a plan that originally called for eight men to be put to death before April 30, when Arkansas' supply of a sedative used in lethal injections expires.

On Monday, Don Davis won a reprieve from the state's top court a few hours before his scheduled execution, then waited almost until midnight to learn the Supreme Court would not allow the execution to proceed. While Davis had spent the past quarter century on death row, lawyers filed multiple emergency appeals at the 11th hour to try to spare his life.

WHY DO SUCH DELAYS TAKE PLACE?

Inmates can spend years, or even decades, appealing their convictions and death sentences in state and federal courts. The average time between sentencing and execution for prisoners executed in 2013 topped 15 years, according to the federal Bureau of Justice Statistics.

By the time an execution takes place or is stopped, often after the inmate has been fed his intended final meal, four or more different courts are supposed to have examined the trial record, legal issues, newly discovered evidence, assertions of innocence and claims of constitutional violations.

And yet inmates plead with varying amounts of success that key elements of their case have never been examined by a court. Lawyers for Arkansas inmate Lee are working at both the state and federal level to get a court to block Lee's execution, scheduled for Thursday. Lee claims blood and hair evidence from his 1993 trial has never been tested and could help prove his innocence. In federal court, Lee said a string of incompetent lawyers failed to make the case that he is intellectually disabled and thus ineligible to be executed.

New issues also arise late in the process, including questions about execution drugs. On Wednesday, inmates asked the U.S. Supreme Court to take the case challenging the use of a sedative used in flawed executions in other states and one of three drugs Arkansas plans to use in its executions. In 2015, justices upheld Oklahoma's execution protocol that used the same drug.

WHAT'S THE PROCESS?

The Supreme Court has the final say on almost every execution, and the justices reject all but a few emergency appeals by inmates.

The justices and their clerks know well in advance when executions are scheduled and where. A court official informally known as the death clerk keeps everyone up to date and communicates often with lawyers for inmates and the states as the date of execution nears.

As lawyers for condemned inmates press the case for delay in state and lower federal courts, the Supreme Court receives information about developments and, eventually, copies of those decisions.

Most often those lawyers press their arguments at the highest court in the country in a final attempt to save their clients' lives. Less often, it's the state that seeks permission to proceed after a lower court has blocked an execution. That's what happened Monday in Arkansas.

WHAT HAPPENS AT THE HIGH COURT?

When those appeals reach the Supreme Court, they go first to the justice who oversees the state in which the execution is scheduled. But death penalty appeals almost always are referred to the entire court.

The justices typically do not meet in person to discuss these cases, but confer by phone, and sometimes through their law clerks, according to the court's guide to emergency applications.

It takes five justices, a majority of the court, to issue a stay or lift one that has been imposed in another court. The overwhelming number of last-minute appeals are denied, and often without comment.

Occasionally, one or more justices will dissent from the decision to let the execution take place. Even more rarely, a justice will explain why.-AP