HERE’S WHAT I think,” Nakazawa said.

     “I’d rather hear what you know,” Schofield cut into his train of thought.

     You’ll have to settle for what I think for now.” Nakazawa didn’t like being interrupted.

     “Just sayin’,” Schofield said, shrugging.

     “I think the accidents were mostly isolated because the perp targeted them through their car radios,” Nakazawa said. “The fact that in the cases where drivers were not listening to their radios there was collateral damage supports this hypothesis.”

     “But then, the perp would have had to know which station each driver was listening to,” Schofield interrupted again. “Either that, or he would have had to modify each radio.”

     “We checked.” Nakazawa said. “No modifications.”

     “OK.” Schofield was sounding more supportive now. “Are you suggesting the perp broke into each car, turned on the ignition, then checked to see what station the radio was set to?”

     “That would be one way of doing it,” Nakazawa allowed.

     “Seems like a lot of work.” Schofield was analyzing it in his head. 

     “We would have found scratch marks on the tumblers if someone tried to pick their way in. And some of those cars have those electronic locks that are damned near impossible to pick.”

     Nakazawa picked up his train of thought. “Then there’s the problem of a driver changing stations once he’s on the road. We think there’s an easier explanation.”

     “I’m all ears.” Schofield leaned a little forward in his chair.

     “Back in World War II, the British intercepted coded radio messages from Russia that were being broadcast into London,” Nakazawa explained. “What they needed was a way to find out who was listening. What they came up with was rather ingenious.

     “They broadcast silence on the same frequency as the coded messages. Then they ‘read’ the frequencies playing out on the antennas in their search area. If the radio attached to an antenna was ‘processing’ that frequency, there would be less of that frequency on the antenna being scanned. But if the radio was tuned to some other frequency, or even turned off, then that frequency would be in abundant supply when the antenna was scanned.”

     “If I may interrupt you,” Schofield said. “You’re saying that by its absence, that frequency would give away the fact that that radio was specifically tuned to that frequency?”

     “Not absence, but certainly a diminished signal.” Nakazawa nodded. “Arbitron used a similar approach back when most TVs got their signals from antennas They would just drive up and down a street with a weird-looking contraption pointed at TV antennas and know precisely what that household was tuned into.”

     “So, you’re saying our perp need only have one of these, how did you put it? Contraptions,” Schofield was on it now. “and he could tell what station a driver was currently listening to?”

     “We believe that’s precisely the way he did it,” Nakazawa confirmed. “That still doesn’t tell us how he used this information.” Schofield reached for his jacket. “But I think we’re headed in the right direction.

     “Good work. Now let’s figure out the ‘how.'”