The Silent Echo. THE ECHO TRACERS, #1

In a near-future D. C. where traditional digital evidence has been compromised by a global hack, the FBI relies on the "unheard." Maren, a 54-year-old acoustic engineer who has spent years in self-imposed isolation, is the only person capable of "tuning" the government's new, experimental scanners. These devices scan the molecular texture of walls and glass to retrieve "trapped" sound waves from the past.
When a high-profile federal judge is found dead inside his soundproofed, high-security panic room-locked from the inside with no signs of entry-the case is ruled a natural heart attack. Only Agent Elias Vance, a veteran investigator in his fifties with a gut feeling that something is wrong, refuses to close the file. He recruits Maren to "hear" what the cameras couldn't see. Together, they discover a terrifying new weapon: Infrasound.
The killer didn't need to enter the room; they used a specific frequency transmitted through the building's plumbing to vibrate the judge's own pacemaker until it failed. As Maren and Elias dig deeper, they realize the judge was only the first target. To stop a "silent" serial killer, they must track a predator who leaves no fingerprints, only a resonance that Maren must find before it's used against them.