Crime is often framed as the good guys versus the bad guys. The Spencer Reids (from “Criminal Minds”) of the world against those caught by violence or stupidity. A fingerprint left behind. A knife ordered from Amazon: Thank you, Bryan Kohberger. But what happens when the murder weapon is invisible?

 Just one week after 9/11, Washington, D.C. faced a new kind of terror: biological. Letters laced with anthrax spores moved through the U.S. postal system. They were sent to media outlets and government offices. The notes read: “WE HAVE THIS ANTHRAX. YOU DIE NOW. ARE YOU AFRAID?” The A’s and T’s — both symbols for DNA nucleotides — were bolded. Investigators speculated whether the killer was sending hidden messages through protein codes.

 The problem? Most detectives don’t study bacteria, so they turned to the experts. One was Bruce Ivins of the U.S. Army Medical Research Institute of Infectious Diseases. Ivins was a senior researcher specializing in anthrax vaccines who had direct access to anthrax spores stored at the lab. But, when he forked over samples from his lab, they didn’t match the deadly strain used in the letters.

 The experts were the suspects. Only government scientists had access to these strains, and, only they could explain what was happening. The people who guided the investigation had the power to twist it. Seven years later, Bruce Ivins was re-examined, and with new information surfacing, he was named the prime suspect. FBI agents said Ivins was, beyond a reasonable doubt, the killer. Ivins was never formally charged; he took his life in July 2008 as the FBI prepared to indict him.

 Five people died in the attacks. Robert Stevens, a photo editor in Florida, was the first. Ottilie Lundgren, a 94-year-old woman in Connecticut, was the last. At least two contaminated letters passed through Brentwood’s mail processing center in Washington, D.C. The facility handled over three million pieces of mail each day. Authorities told workers they were safe. Yet hazmat-clad men searched the building side by side with unprotected postal employees. Two postal workers died asking the obvious: If the experts need suits, why don’t we?

 Government negligence was not unique to anthrax. It echoed years later in Hurricane Katrina. Bodies decomposed on rooftops. Millions of Americans struggled to survive without water and shelter. A clip shows Anderson Cooper floating past a corpse in a boat. He got there before the military. As for the Anthrax attacks, the Senate buildings shut down within two hours of anthrax detection. The post office took 40 hours. “The dogs got Cipro [antibiotic] on Capitol Hill before we did,” one former postal worker said.

“The people who guided the investigation had the power to twist it.”

 In my Infectious Diseases class, we recently examined anthrax under a microscope. The spores sat between two thin glass slides, smaller than a square inch. It was almost impossible to believe. The invisible bacteria sandwiched on the glass was the same weapon that killed five people. It was surreal to think about how the contents between these little glass plates sent fear through the veins of America.

 We worry about knives and guns. But these weapons are visible; they can’t compare to the danger of what we cannot see.

 It’s comforting to imagine that the good guys always solve the case. That the truth is only a matter of piecing evidence together. But there is a fine line between genius and psychopath: Sometimes, they overlap.