Bonnie shook her head. Her long braid swung from side to side like a rope. “I’ve taken it as far as I can,” she said. “I can make the images bigger, but I don’t have the software necessary for the sort of filtering that would make them any sharper. You should try one of the Japanese firms. Sony, or Hitachi. They should have the computers geared up for it. Or you could try firms working on artificial intelligence or robotics.”

“Robotics?” queried Howard.

“Robotics companies are big on artificial intelligence, and that’s the sort of expertise you’ll need. The pictures can be cleared up further by the application of algorithms using what are called the Hough Transform and Fourier Transform, and I can tell you which experts would be able to do that. A computer with some form of artificial intelligence could compare adjoining pixels and correct for abnormalities based on an assumption of what it’s looking for.”

Howard frowned. “I don’t follow.”

“Well, if the computer knows it’s looking at a face, it will know that an eye has a certain shape, so has a nose, so has a chin. It has to know whether a dark patch is a moustache, a nostril, or the pupil of an eye. It has to know that human bodies are made up of curves, but that mechanical objects are usually flat surfaces. If it’s looking at a licence plate, for instance, it must know to look for numbers and letters and not abstract shapes. I’m sorry, Agent Howard, I’m not explaining this very well.”

“Cole,” he said, “please call me Cole. And you’re doing just fine. Actually, I know someone who has access to the sort of technology you’re talking about.”

“Really?” she said. “Who would that be?”

“Clayton Electronics.”

Bonnie raised her eyebrows. “They’re good. Of course, their head office is in Phoenix, I’d forgotten. Why didn’t you go to them first?”

Howard stacked the photographs together and slid them back into the file. “We wanted to keep it within the FBI as much as possible. You’ve seen the video, you know what the implications are.”

Bonnie lowered her eyes and her cheeks reddened like a guilty schoolgirl. Howard wanted to ask her what was wrong but felt that she’d shy away from such a direct approach. He waited for her to tell him what was troubling her.

“I had an idea,” she said, still avoiding his eyes. “Well, not my idea, really. It was my husband’s.”

“Your husband?”

She nodded and raised her head. “He’s a mathematician. A PhD. He specialises in computer graphics.”

Howard was bemused, but he listened attentively. Bonnie Kim was clearly very intelligent and anything she had to offer on the case could only be of help.

“I was explaining about the video, about the three men with rifles and the towers, and he said it would make an interesting computer model. You could program the coordinates of the men and the targets, and get a 3-D structure representing their positions.”