By Thanh Truong, NBC News Correspondent

JACKSON, Ga. – On Highway 36 in Jackson, Ga. the truck stop across from the Georgia Diagnostic Prison is a busy place. On Wednesday morning truckers were gassing up; commuters were getting their coffee. For the most part it's an average day. But at 7 p.m. this evening, death row inmate Troy Davis is scheduled to die by lethal injection inside the prison.
 
In the days leading up to Wednesday's execution, supporters of Davis staged mass marches, protests and rallies. Those calling for a halt to his execution include everyday people, death penalty advocates and opponents alike, from President Jimmy Carter to Pope Benedict. All of them saying there's too much doubt about Davis guilt for the state to move ahead with the execution.
 
Davis was convicted for the 1989 murder of Savannah police officer Mark MacPhail. At the time, MacPhail was off duty working a security detail. Investigators say as he got off his shift, MacPhail came across a homeless man being attacked. According to police, MacPhail went to his aid but was shot in the face and chest.

Witnesses put Davis and another man at the Burger King parking lot in Savannah. They testified Davis was the triggerman. Prosecutors presented shell casings at the trial. They said those casings matched those of a previous shooting earlier that night. Davis was convicted in that previous shooting. In 1991, Davis was convicted for the MacPhail murder and was sentenced to death.  

Years of appeals
Davis has maintained his innocence through the years. Seven of the nine witnesses who testified against Davis later recanted or changed their statements. Several claimed police coercion. One of those witnesses, Jeffrey Sapp, said, "I got tired of them harassing me… I told them that Troy told me he did it, but it wasn’t true… I didn’t want to have any more problems with the cops, so I testified against Troy." 
 
Davis' defense also claims a lack of physical evidence. The murder weapon was never recovered.  All of it was presented during previous appeals and attempts at a retrial. Those attempts failed.

Prosecutors have been resolute. Joining them are the police and family of MacPhail. All say they have no doubt that Davis is the killer and deserves death.       

Davis had one last chance at clemency on Monday.  The Georgia Pardons and Parole Board heard from both the defense and prosecution. On Tuesday it denied Davis clemency. With virtually all of his legal options now exhausted, Tuesday's decision was seen as the one final shot to have Davis's sentence commuted to life in prison instead of death. Georgia's governor can not intervene. 

Two different visions of justice
Now in a matter of hours, the years of appeals, moral debates about the death penalty and pleas from both families will come to a head. I've spoken to relatives of both Davis and MacPhail. All want justice, but their visions of justice differ. 

Before the clemency hearing Davis's nephew, DeJuan Davis-Correia told me the justice they were seeking would help both families.

“We have the utmost respect for that family. I also pray at night for that family. We hope they find understanding in their hearts that we are actually trying to get the wrong person out of jail and the right person in," said Davis-Correia. 

Following Monday's hearing the family MacPhail left behind expressed their feelings. Joining his widow Joan, were his son, daughter and mother. After years of delays and hearings, they said they were thirsty for justice, not blood.

“We have lived this for 22 years. We know what the truth is and for someone to ludicrously say he [Davis] is a victim? We are the victims. Look at us. We have put up with this stuff for 22 years and it's time for justice today," said Joan MacPhail

Davis has declined to request a specific last meal.  

SEAN GARDNER / Reuters

Freddie Walker stacks sandbags to protect Ergon Marina along the Mississippi River in Vicksburg, Mississippi on Tuesday.

By Thanh Truong, NBC News Correspondent

VICKSBURG, Miss. – Austin Golding is the third generation in his family making a living off the Mississippi River.

Back in 1967, his grandfather founded Golding Barge Line. The company moves millions of pounds of product (mostly petroleum) up and down the river each year – but now its office in Vicksburg is surrounded by water. We met him as he gave us a lift in a boat across what used to be the office's parking lot.

"I was raised around this river, and I've never seen it this high. No one alive has seen it this high. When you're around the water this much you learn to respect the river and its power real quick," he said.

With his bright blue eyes and youthful face, the 25-year-old spoke with a tone of experience you would expect to hear coming from a river man twice his age. But he and most people in Vicksburg know the potential for flooding. The Mississippi River and Yazoo River meet in Vicksburg. The city expects to see the water rise to levels not seen since 1927.

"This is going to be an epic flood. I just pray that the infrastructure that's in place and the work that's been done will protect us," said Golding.

Scott Olson / Getty Images

Jermaine Jarrett paddles a boat down a flooded street in his neighborhood on Monday in Memphis, Tenn. Click on the photo to see a slideshow of the floods across the U.S.

There are temporary flood walls along the levees near downtown; water though is already seeping through those walls. Low-lying areas along the Yazoo River have already had roads swallowed by rising water. The worst flooding isn't expected for at least another week.

"We'll be here, we're not going anywhere. This is our life. This river has given us so much but when it comes – you just get the hell out of its way," Golding said.

Mighty Mississippi crests in Memphis