“The number one choice among terrorists. It's military. You can't buy it from commercial demolition suppliers. It looks like dirty white putty, kind of oily. You can mold it real easily.”

“Was it like hooked to a clock or something?”

Healy walked to his attaché case and picked up one of the plastic bags. It contained bits of burnt metal and wires.

“Junk,” Rune said.

“But important junk. It tells me exactly how the bomb worked, how she was killed. It was in the phone she called from. Which was on a wooden desk right about there.” He pointed to a space on the floor near the crater. “The phone was a new-model Taiwanese import. That's significant because in the old Western Electric phones most of the space was take up by the workings. There's a lot of empty space in new phones. That let the killer use about a half pound of C-4.”

“That's not so much.”

Healy smiled grimly. “Oh, yes it is — C-4's about ninety-one percent RDX, which is probably the most powerful nonnuclear explosive around. It's a trinitramine.”

Rune nodded, though she had no idea what that was.

“They mix that with a sevacate and an isobutylene, oh, and a little motor oil — those are for stability, so it doesn't go off when you sneeze. You don't need very much at all for a very, very big bang. Detonation rate of about twenty-seven thousand feet per second. Dynamite is only about four thousand.”

“If you haven't sent it to the lab how do you know it's C-4?”

“I pretty much knew when I walked in. I could smell it. It was either that or Semtex, a Czech explosive. I also found a bit of plastic wrapper — with a U.S. Army code on it. So it'd have to be C-4, and old C-4 because it didn't completely detonate.”

“What set it off?”

He was absently examining burnt pieces of metal and plastic in the bag, squeezing them, sliding them around.

“The C-4 was molded around an electric detonating cap attached to a little box that contained a battery and a radio receiver. The wiring was also connected to the switch that closes the circuit on the phone — so the device wasn't armed until someone picked up the receiver. That's the problem with radio detonation. You always run the risk that somebody, police or fire or a CB operator, will hit your frequency by mistake and set the charge off while you're planting it. Or when there's somebody in the room you don't want to kill.”

Rune said, “So Shelly picked up the phone, called the number, and whoever was on the other end — what? — used a walkie-talkie to set it off.”

“Something like that.” Healy was staring out the window.

“And that's the phone number your friend's trying to find out.”

“Only he's not as enthusiastic as he ought to be.”