BOSTON (CBS) – Twenty five years after the murder of a Boston detective, the Suffolk County District Attorney’s Office announces it will drop the case against the man suspected of the killing.

“My office today will file paperwork ending the prosecution of Mr. [Sean] Ellis for first degree murder and armed robbery,” said District Attorney John Pappas Monday afternoon.

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Pappas says the current state of the evidence in the case will “make it unlikely to prevail in a new trial.”

Suffolk County District Attorney John Pappas (WBZ-TV)

Adding that in addition to the corruption linked to the case, foggy eyewitness testimony would prove to be a challenge. “The state of witnesses memory today, 25 plus years later, would present a tremendous challenge to us in a retrial,” Pappas said.

In 1995, Sean Ellis was sentenced to life in prison for the 1993 shooting death of Det. John Mulligan. Ellis was 22.

By 2015, 20 years into his sentence and three trials later, the state’s highest court upheld a lower court ruling — which found “corrupt detectives were involved in nearly every aspect of the homicide investigation that led to Ellis’ prosecution.” Ellis’ conviction was overturned.

Sean Ellis (WBZ-TV)

Today, at the age of 44 he maintains his innocence and says he’s relieved.

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“I’m ecstatic to say the least,” Ellis said inside his lawyer’s office hours after learning of the development. “The past few hours have been an array of emotions. I’m extremely happy.”

Still, prosecutors say the decision to dismiss, although a difficult one, is not an exoneration.

“His conviction for possessing the murder weapon and Det. Mulligan’s service weapon, which was stolen from his body, remain undisturbed to this day,” said Pappas.

Sean Ellis was convicted of first-degree murder in 1995. (WBZ-TV file image)

Ellis’ attorney says the DA’s office is unwilling to admit the corruption within the city’s police department in the 90’s.

“The idea that they’re saying that they’ve uncovered no evidence that anyone else did it. It’s kind of hard to find evidence if you’re not looking,” said attorney Rosemary Scapicchio.

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Ellis says he’s looking forward to his new found freedom and wants to attend college.

Anaridis Rodriguez