It would have been his 7th -- SEVENTH! -- trial.  The AP covers the decision here:
A Mississippi man 
freed last year after 22 years in prison will not be tried a seventh 
time in a quadruple murder case, a judge ruled Friday after prosecutors 
told him they no longer had any credible witnesses. 
Curtis
 Flowers was convicted multiple times in a bloody slaying and robbery at
 a small-town furniture store in 1996. The U.S. Supreme Court threw out 
the most recent conviction in June 2019, citing racial bias in jury 
selection.
“Today,
 I am finally free from the injustice that left me locked in a box for 
nearly twenty three years,” Flowers said in a statement released by his 
lawyer. “I’ve been asked if I ever thought this day would come. I have 
been blessed with a family that never gave up on me and with them by my 
side, I knew it would.”
Montgomery County 
Circuit Judge Joseph Loper signed the order Friday after the state 
attorney general’s office, which had taken over the case, admitted the 
evidence was too weak to proceed with another trial.
“As
 the evidence stands today, there is no key prosecution witness ... who 
is alive and available and has not had multiple, conflicting statements 
in the record,” Assistant Attorney General Mary Helen Wall wrote in a 
filing presented to Loper on Friday. 
 Vangela Wade, one of Flowers' current lawyers, wrote an op-ed in the Washington Post.  It starts this way:
Nearly 23 years.
 More than 8,000 days. That’s how long Curtis Flowers — a Black man who 
was tried an astonishing six times for the same crime — was locked away 
in a cramped jail cell with little ability to see his family. Until 
Friday, when Mississippi’s attorney general decided to drop the charges, Flowers was waiting to find out whether he would be subjected to yet another trial.
My
 organization, the Mississippi Center for Justice, has been defending 
Flowers since summer 2019, working with the team of lawyers that has 
represented him for many years. We are thrilled that he will finally go 
free. The accusations against Flowers were never grounded in facts, but 
rather fueled by improper conduct by Montgomery County District Attorney Doug Evans — the prosecutor in each of Flowers’s six trials.
Unfortunately,
 the Flowers case offers just a tiny snapshot of prosecutorial 
misconduct. Such misconduct — which can include introducing false 
evidence, using dubious informants, withholding evidence that could 
exonerate the defendant or discriminating in jury selection — puts 
countless innocent people behind bars. As a former prosecutor — notably,
 the only Black staff member in the office — I witnessed firsthand the 
disproportionate number of African Americans entangled within the 
criminal justice system.
Prosecutors
 wield enormous control over the criminal justice system. They determine
 which charges to pursue  — if any — and make recommendations on bail, 
pretrial incarceration and sentencing, which are often accepted by 
judges. In each of these instances, prosecutors have the potential to 
abuse civil rights — with few, if any, consequences.
One analysis
 by the Innocence Project of 660 cases in which courts confirmed 
prosecutorial misconduct revealed that the prosecutor was ultimately 
disciplined in only one. Another report of 707 cases of prosecutorial misconduct in California found that just six prosecutors were disciplined.