Madeline Singas, the Nassau County district attorney, said in a statement that her office had obtained a protective order for Mr. Rodriguez in December 2018, but that his identity had been disclosed to defense lawyers in December 2019 under a judge’s order.

Judge Helene F. Gugerty of Nassau County Court is presiding over the case. A spokesman for the state court system did not immediately respond to a request for information about why the order had been issued.

While Ms. Singas did not specifically cite the new law as contributing to Mr. Rodriguez’s death, she suggested in her statement that being forced to identify him well before trial had hampered the authorities’ ability to protect him, and may have cost him his life.

“This courageous man was prepared to testify against alleged assailants at an upcoming trial, but he was brutally beaten to death before he could,” Ms. Singas said in the statement, adding that the case “underscores the importance of safeguarding the identities of witnesses and victims of crimes.”

Patrick Ryder, the Nassau County police commissioner, echoed that sentiment at a news conference.

“This man’s dead because we didn’t do enough,” Commissioner Ryder said, according to Newsday. He added, “This law is not helping us.”

He said that the trial in the case was originally scheduled to begin on Jan. 6, but did not. After that, he said, a “pattern of intimidation” against Mr. Rodriguez began.

“That protective order, because of the new changes in the law, was lifted,” he said. “We don’t know if the defense counsel turned that info over to the defendants.”