For decades, Isaiah Andrews has maintained his innocence in the 1974 murder of his wife, unaware that the key to his exoneration was buried in the archives of the Cleveland Division of Police.

The Cleveland police’s decision to withhold crucial information in the case resurfaced on Thursday, when an Ohio Court determined that Mr. Andrews, now 84, had been wrongfully imprisoned for 45 years.

Mr. Andrews, who is sick and uses a wheelchair, has been free since May 2020. He was later found not guilty at a second jury trial in October, but the court had to declare him wrongfully imprisoned so he could seek damages from the State of Ohio.

“I’ve won the battle for this,” Mr. Andrews told reporters after the court hearing on Thursday.

Mr. Andrews and his wife, Regina Andrews, were newly married when he reported her missing from the Cleveland hotel room that they had been living in while they looked for a permanent home, according to court documents.

On Sep. 18, 1974, Mr. Andrews told detectives that he last saw her just before 8 a.m. that day and that he had been running errands into the evening, according to court documents.

Ms. Andrews’s body was found that afternoon in Forest Hill Park by a worker on his lunch break. She had been stabbed multiple times and wrapped in bedroom linen.

At the time of the murder, detectives wrote that they thought the crime was committed by Willie H. Watts, who was trying to sell his mother’s valuables to get away from the city, according to court documents. He was arrested, but his name was not mentioned in the trial and there was no indication that he was mentioned in the case discovery, according to the court papers.

Detectives produced no physical evidence linking Mr. Andrews to his wife’s murder, and the police found no blood in his car or hotel room, but he was convicted and sentenced to life in prison in 1975. He had previously served 15 years in prison for the murder of his staff sergeant in the Marines, according to the Cuyahoga County Prosecutor’s Office.

Investigators released Mr. Watts after he provided an alibi for the time of death initially estimated by the coroner, court papers said. The estimate was revised after an autopsy.

Later, Mr. Watts was charged on four separate occasions with kidnapping and was imprisoned for more than 20 years for aggravated arson. Two of the kidnapping cases were later dismissed. Mr. Watts died in 2011, Cleveland.com reported.

The Ohio Innocence Project, which aims to get wrongfully convicted people out of prison, did not know about Mr. Watts when it decided to review Mr. Andrews’s case in 2015.

“You would have never known from reading the trial transcripts that the police had arrested someone else for this,” said Brian Howe, a staff attorney for the project.

That information became available only in 2019, after Mr. Andrews’s lawyers requested that the DNA in the case be tested. The Ohio Bureau of Criminal Investigation requested files from the original medical examination and was given police files which brought to light the other man’s arrest.

A judge for the Cuyahoga County Common Pleas Court reversed Mr. Andrews’s conviction in 2020 and ordered a new trial.

Mr. Andrews’s lawyers said that the retrial was unnecessary and that they were surprised the Cuyahoga County prosecutors decided to pursue it instead of declining to prosecute.

The prosecutor’s office said in an emailed statement that it had weighed Mr. Andrews’s previous murder conviction in its decision to pursue a retrial. “When this conviction was overturned, we had an obligation to pursue justice on behalf of the victim and her family,” the statement said.

At the second trial in October, the proceedings mostly involved reading aloud transcripts from the initial trial in March 1975. The jury found him not guilty.

Mr. Andrews’s wrongful imprisonment is considered the third longest known in the United States, according to the National Registry of Exonerations.

The wrongful imprisonment declaration on Thursday allows Mr. Andrews to continue with a lawsuit that seeks damages from the state.

Mr. Andrews also filed a federal civil rights lawsuit against the City of Cleveland in February, accusing the police there of failing to provide information about the other suspect.

Sarah Gelsomino, a lawyer with Friedman, Gilbert and Gerhardstein who is representing Mr. Andrews, said that under state law, he was entitled to $56,752.36 for each year that he was imprisoned, or more than $2.5 million. The lawyers will also seek money for lost wages, legal fees and the costs of proving his innocence.

The money cannot make up for the years Mr. Andrews spent in prison, however.

“He lost everybody when he was in prison,” Ms. Gelsomino said. “So, he didn’t have a family waiting to welcome him back.”

Instead, Mr. Andrews has been supported by a community of other people who have been exonerated in Ohio or who are still seeking exoneration. The Ohio Innocence Project has freed 34 individuals, including 14 cases that originated in Cuyahoga County, since it was founded in 2003.

Three members of that community sat behind Mr. Andrews in court on Thursday: Lamont Clark, Ruel Sailor and Charles Jackson, who was exonerated in November 2018 after 27 years in prison and who lives with Mr. Andrews and helps care for him.

The men told reporters after the hearing on Thursday that it was a day for them all to celebrate.