“H'm! I don't say you've much to go on, but there's certainly more here than there was in the other tourniquet. The banjo-string's not much help, of course; one can buy 'em in any musical-instrument shop. But the rubber tubing might suggest something to you.”
Inspector Flamborough scrutinised it afresh.
“It's very thick-walled, sir, with a much smaller bore than one would expect from the outside diameter.”
Sir Clinton nodded.
“It's what they call ‘pressure-tubing’ in a chemical laboratory. It's used when you're pumping out vessels or working under reduced pressures generally. That's why it's made so thick-walled: so that it won't collapse flat under the outside air-pressure when you've pumped all the gas out of the channel in the middle.”
“I see,” said the Inspector, fingering the tubing thoughtfully. “So it's the sort of thing one finds in a scientific place like the Croft-Thornton Institute?”
“Almost certainly,” Sir Clinton agreed. “But don't get too sure about your rubber tubing. Suppose someone is trying to throw suspicion on one of the Croft-Thornton staff, wouldn't this be an excellent way of doing it? One can buy pressure-tubing in the open market. It's not found exclusively in scientific institutes, you know.”
Flamborough seemed a shade crestfallen at the loss of what he had evidently regarded as a promising line.
“Oh, indeed?” he said. “I suppose you're right, sir. Still it's a bit uncommon, isn't it?”
“Not what you'd expect the ordinary criminal to hit on straight off, I suppose you mean? But this fellow isn't an ordinary criminal. He's got plenty of brains. Now doesn't it strike you as strange that he should go to the trouble of leaving this tourniquet for your inspection? He could have slipped it into his pocket easily enough and it wouldn't have bulged much.”