The defense argued that prosecutors had failed to show how the drugs had been contaminated or to specify any role that Mr. Cadden might have played in the deaths. On Wednesday, Mr. Cadden’s lawyer, Bruce A. Singal, pushed back against Mr. Weinreb’s comments, saying his client had not been convicted of massive fraud.

“It was a terrible lapse of judgment for the U.S. Attorney’s Office to accuse Mr. Cadden of murder in the first instance,” Mr. Singal wrote in an email. “For the prosecution to persist in trying to blame him for the deaths in the wake of acquittals on all 25 murders is irresponsible and reprehensible.”

Legal specialists said the burden of proof for the murder charges was ultimately too high.

“They were going to have to show that the pharmacist knew, or recklessly disregarded, that the vials they were shipping were going to cause infection or kill people,” said Kevin Outterson, a law professor at Boston University.

“You can have a bad lab that is sloppy, and you might know that you’re cutting corners to save money,” Mr. Outterson said. “That is completely different from somebody knowing their vials were contaminated and still shipping them nonetheless.”

Family members of the victims and survivors of the infections said they were dismayed that Mr. Cadden had not been convicted of murder.

“He was leveraging profit by not maintaining a proper facility, a sanitary facility,” said Bob Bergeson, 59, whose sister, Diana Reed, died of fungal meningitis during the outbreak, leaving behind a husband with amyotrophic lateral sclerosis who now lives by himself. “That’s murder in my mind.”

Angel Farthing, 46, who was sickened with meningitis and now has scar tissue on her spine, said other survivors had expressed their frustration over the verdict in a private Facebook group. She said she still hoped that Mr. Cadden would spend years in jail.