NEWTON, Mass. — The mayor of Holyoke, Mass., got an unsigned letter over the weekend that deeply disturbed him.

“Are you aware of the horrific circumstances at the Soldiers’ Home?” the letter read, and went on to describe serious breaches, like a resident suspected of having the coronavirus, awaiting the results of a test, being sent back to a dementia ward with 20 other veterans.

“Where is the state in addressing what is truly happening in this building?” the letter concluded.

The mayor, Alex Morse, reached out to Bennett Walsh, the superintendent of the Holyoke Soldiers’ Home, a 247-bed, state-managed nursing home for veterans, to figure out what was going on.

But by then, Mr. Morse said, the damage was far more than he had imagined: In a matter of five days, eight veterans had died, apparently without being reported to either state or local officials. Others were sick with the coronavirus; staff members were too.