The remark suggested many things to me. Was it that he meant to
imply that, after all, the missing Betty Blackwell had had
something to do with it? In fact, could the thing have been done
by a woman?

"Most persons," remarked Craig, as he studied the marks on the
door, "don't know enough about jimmies. Against them an ordinary
door-lock or window-catch is no protection. With a jimmy eighteen
inches long, even an anemic burglar can exert a pressure
sufficient to lift two tons. Not one door-lock in ten thousand can
stand this strain. It's like using a hammer to kill a fly. Really,
the only use of locks is to keep out sneak thieves and to compel
the modern, scientific educated burglar to make a noise. This
fellow, however, was no sneak thief."

He continued to adjust the machine which he had brought. Langhorne
watched minutely, but did not say anything.

"Bertillon used to call this his mechanical burglar detector,"
continued Kennedy. "As you see, this frame carries two
dynamometers of unequal power. The stronger, which has a high
maximum capacity of several tons, is designed for the measurement
of vertical efforts. The other measures horizontal efforts. The
test is made by inserting the end of a jimmy or other burglar's
tool and endeavouring to produce impressions similar to those
which have been found on doors or windows. The index of the
dynamometer moves in such a way as to make a permanent record of
the pressure exerted. The horizontal or traction dynamometer
registers the other component of pressure."