now, he knew.

As calmly as he had spoken thus far Muller continued. "For twenty
years I have been studying the hearts of criminals like yourself.
But there are things I do not understand about this case and it
interests me very much."

Langen had wiped the drops from his forehead and he now turned on
Muller a face that seemed made of bronze. There was but one
expression on it, that of cold scorn.

"I feel greatly flattered, sir, to think that I can offer a problem
to one of your experience," Langen began. His voice, which had been
slightly veiled before, was now quite clear. "Ask me all you like.
I will answer you."

Muller began: "Why did you wait so long before committing the
murder? and why did you drag your victim from place to place when
you could have killed her easily in the compartment of the railway
train?"

"The windows of the compartment were open, my honoured friend, and
it was a fine warm evening for the season, because of which the
windows in the other compartment were also open. There was nothing
else I could do at that time then, except to offer Asta a cup of
tea when she felt a little faint upon leaving the train. I am a
physician and I know how to use the right drugs at the right time.
When Asta had taken the tea, she knew nothing more until she woke
up a day later in a room in the city."