Editor's note: A retrial of Iwao Hakamada, 88, who had been incarcerated for nearly half a century on murder charges, is to conclude on May 22. Before the retrial’s last hearing, we shine a spotlight on letters he wrote on death row in a four-part series. This is the first installment.

The odds were always stacked against Iwao Hakamada.

Prosecutors in Japan have a 99-percent conviction rate for individuals charged with crimes. And for inmates who insist they are innocent, getting a court to grant a retrial has been extremely rare.

Hakamada, 88, is also fighting against time to clear his name. He was recognized by Guinness World Records as the longest serving death row inmate.

The former professional boxer was 30 when he was arrested on suspicion of murdering four people--a manager of a miso manufacturer and three members of his family--robbery and arson in 1966.

The Supreme Court in 1980 finalized his conviction and death sentence.

But in 2014, a district court accepted Hakamada’s second appeal for a retrial, citing the possibility that key evidence against him had been fabricated.

The court also ordered Hakamada’s release, ending his incarceration spanning more than 47 years.

However, the time on death row took a heavy toll on his mental condition.

For his retrial, which started in October, Hakamada is not required to appear in court because he is not deemed mentally fit to give credible testimony.

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HAMAMATSU, Shizuoka Prefecture--Eight plastic trays holding thousands of letters in various stages of decay sit in a closet of an apartment here in central Japan.

Some of the letters have yellowed with age. Others have gathered mold.

The letters were written by Iwao Hakamada mainly to his family between 1967, when he first stood trial at the Shizuoka District Court, and 1995, when he was fighting for a retrial as a death row inmate.

The letters are now kept at the home where Hakamada and his sister, Hideko, live.

In mid-October, just before the retrial started, Hideko, now 91, placed the letters on a table at their apartment.

“Iwao never stopped writing, seizing every opportunity available,” said Hideko, who has waged a tireless campaign for her brother’s release. “I have kept and bound his letters together. That is something I thought I can do for him.”

Although the subject matter varied, and Hakamada’s mental illness was apparent in his later letters, one thing remained consistent throughout his decades of correspondence: He always maintained his innocence.

“God. … I am innocent. I shout this every day, praying with all my heart that what I am crying out will ride the wind from Shizuoka to reach the ears of people outside.” (Around January 1967)

His early letters were addressed to his mother. But after her death, he wrote mainly to Hideko. Other relatives and defense lawyers who received letters from Hakamada entrusted Hideko to preserve them.

After he was imprisoned, Hakamada learned pen calligraphy, one of the things he took up to pass the time.

Some letters showed the masterful handwriting skills he acquired behind bars. But in other letters, his longhand was “just flowing,” said Hideko.

He seemed preoccupied with unloading everything from his heart, rather than paying attention to how his handwriting looked.

“Even when I reread those letters, I never got sentimental,” Hideko said. “I’ve had much bigger things to worry about.”

Locked up in prison, Hakamada could only find solace when he met his family members.

In his letters, he described how encouraged he felt when his relatives visited him and how much he looked forward to their next visits.

Hideko made it a point to see him regularly. She wanted him to know that his family would never give up on him.

She recalled that on one visit, the time flew by because Hakamada spoke nonstop, leaving her time only to nod.

Nevertheless, she was heartened that he was in good spirits.

Hideko had also sent him money for buying daily necessities in prison.

In one letter at the end of the text, Hakamada scribbled down in small letters: “Please send me 3,000 yen” ($20).

In another letter that arrived at the end of the same month, he listed items he had bought with the money-- bananas, milk coupons and toilet paper. He added, “Thank you.”

He seemed hopeful that the truth would emerge in the judicial process.

“I, too, believe that it is extremely difficult for humans to try other humans. There are many mistakes in the world. I would like the court to try my case earnestly.” (Around April 1967)

A team of Asahi Shimbun reporters studied more than 2,000 pages of his letters after obtaining permission from Hideko and others in their possession to trace his life in incarceration.

His thousands of letters are now invaluable testimonials about his thoughts and feelings during his long battle for vindication.

The letters show a roller-coaster ride of emotions: hopeful of being found innocent, devastated by being sentenced to death, and encouraged by supporters campaigning for his freedom.

But his declining mental health became reflected in his writing. Toward the end of his incarceration, his letters contained paranoid ramblings about his battles against the devil and painful electrical existences.

(This article was written by Yuri Murakami and Ryuichiro Fukuoka.)

For details of Hakamada's trial and letters, check out https://www.asahi.com/special/hakamadaletters/en/