On the evening of April 21 in Building 21 at the Fishkill Correctional Facility, Samuel Harrell, an inmate with a history of erratic behavior linked to bipolar disorder, packed his bags and announced he was going home, though he still had several years left to serve on his drug sentence.

Not long after, he got into a confrontation with corrections officers, was thrown to the floor and was handcuffed. As many as 20 officers — including members of a group known around the prison as the Beat Up Squad — repeatedly kicked and punched Harrell, who is black, with some of them shouting racial slurs, according to more than a dozen inmate witnesses.

“Like he was a trampoline, they were jumping on him,” said Edwin Pearson, an inmate who watched from a nearby bathroom.

Harrell was then thrown or dragged down a staircase, according to the inmates’ accounts. One inmate reported seeing him lying on the landing, “bent in an impossible position.”

“His eyes were open,” the inmate wrote, “but they weren’t looking at anything.”

Corrections officers called for an ambulance, but according to medical records, the officers mentioned nothing about a physical encounter. Rather, the records showed, they told the ambulance crew Harrell probably had an overdose of K2, a synthetic marijuana.

He was taken to St. Luke’s Cornwall Hospital and at 10:19 p.m. was pronounced dead.

In the four months since, state corrections officials have provided only the barest details about what happened at Fishkill, a medium-security prison in Beacon, New York, about 60 miles north of New York City. Citing a continuing investigation by the State Police, officials for weeks had declined to comment on the inmates’ accounts of a beating.

An autopsy report by the Orange County medical examiner, obtained by The New York Times, concluded that Harrell, 30, had cuts and bruises to the head and extremities and had no illicit drugs in his system, only an antidepressant and tobacco. He died of cardiac arrhythmia, the autopsy report said, “following physical altercation with corrections officers.”

The manner of death: Homicide.

No officers have been disciplined in connection with the death, officials said. A classification of homicide is a medical term that indicates the death occurred at the hands of other people, but it does not necessarily mean a crime was committed.

Inmate witnesses at Fishkill said they are the ones who have been punished. Several described being put into solitary confinement and threatened with violence after speaking with Harrell’s family, their lawyers and with news reporters.

The prison building where Harrell died has long been singled out as a violent place. In 2013, the Correctional Association of New York, a 171-year-old inmate advocacy group with a legislative mandate to inspect New York state prisons, published a report documenting “harassment and provocation” by officers working in Building 21 from 3 to 11 p.m. This was the same time frame when Harrell died. The association found similar problems in 2005.

Five weeks before Harrell’s death, David Martinez, an inmate in Building 21 who was serving time for attempted murder, filed a grievance that said he was being assaulted and harassed by officers. In a subsequent letter, he described them as “a group of rogue officers” who “go around beating up people.”

In July, another inmate, Rickey Rodriguez, said that officers beat him so severely that he lost his two front teeth and had to be hospitalized. Interviewed a little more than a week after he was released from prison, Rodriguez, who was serving time for attempted murder, was still covered with cuts and bruises.

“They go out of their way to pick and choose to beat on guys,” he said.

The State Police plan to turn over the evidence gathered to the Dutchess County district attorney’s office “in the very near future,” said Beau Duffy, an agency spokesman. The corrections department said it was cooperating with the State Police.

“Anyone found to have engaged in any misconduct or in any legal violations will be disciplined and prosecuted,” the department said in a statement.

The Times pieced together the events leading to Harrell’s death from 19 affidavits and letters written by inmates. Most of the inmates shared their affidavits on the condition that their names not be used, because they said they feared retribution from corrections officers.

According to Luna Droubi, a lawyer for Harrell’s family, at least nine of the inmates who saw what happened had been placed at some point in solitary confinement. She said her firm would soon file a lawsuit in connection with the death, and that there was a need for the appointment of a special prosecutor to investigate.

Inmate witnesses are typically viewed with skepticism by investigators, but the accounts from Fishkill are strikingly consistent.

James Miller, a spokesman for the corrections officers’ union, the New York State Correctional Officers & Police Benevolent Association, said in an email last month that Harrell was “acting violently and appeared delusional as a result of apparently ingesting drugs.” While trying to subdue him, one guard had several ribs broken, Miller said.

On Monday, Miller wrote in an email that the union was “reviewing all the facts before rushing to judgment.”

“Rather than simply relying on allegations made by a handful of violent convicted felons,” he wrote, “we will continue to work with our partners in law enforcement to ensure a resolution to this tragic incident.”

Harrell had served several stints in prison for drug crimes starting in 2002. He had five disciplinary infractions while incarcerated, including one days before his death for possessing contraband, according to prison records. None involved violence.

None of the affidavits or letters mentioned Harrell’s fighting back or speaking during the encounter. Several said that once he was on the floor, handcuffed, he stopped moving, and a few of the inmates speculated he may have already been dead by then. While Harrell lay still on the floor, officers periodically walked by, kicking him and hitting him, Ibrahim Camara, an inmate, said in a phone interview.

Most of the inmates could identify the officers involved by last names only. In a database of New York state employees, there are several Fishkill officers who appeared to match the guards most often named by the inmates as being directly involved in the encounter. They are Thomas Dickenson (named by 10 of the inmates), John Yager (10), Robert Michels (9), Bryan Eull (5) and a white woman they knew only as “Ms. B” (4). They also identified the ranking officer at the scene as Sgt. Joseph Guarino. Neither the corrections department nor the union would confirm the names of the officers. Reached by phone, several of the officers declined to comment. Others did not respond to messages.

Through the years, Guarino, 60, has been sued several times by inmates accusing him of brutality. One case was settled by the state in 2012 for $60,000 and another in 2011 for $65,000. In a 2011 deposition, he said inmates typically filed about 30 grievances against him a year and referred to him by the nickname Sgt. Searchalot.

Guarino confirmed he was present that night but said he could not comment.