By The Book

The only thing the police had to go on was the book. It was the one and only clue to the death of the young woman who lived alone in the apartment above the alley. Not a nice neighbourhood but that wasn't reason enough to be killed.
She'd been found by a friend earlier that evening. There was some evidence of a struggle but the body was unmarked except for a bruise on the left side of her head.
Whoever did it used the book to deliver the fatal blow. The corner was clearly dented and some of the victim's hair was embedded in the cover.
The investigating officers concluded that it was probably a lover's quarrel, but Chief Coltrane wasn't convinced.
"You say the book was the murder weapon?" He levelled his gaze at the junior officers.
"That's right sir."
"She have a boyfriend?"
"Still looking, sir, but the friend says she wasn't seeing anybody on a regular basis."
"Interesting," mused the Chief. He thought for a moment. "You hotshots get the name of the book?''
The officers looked around sheepishly. Then one of them said, "I might have it in my notes."
He took out his pad and thumbed the pages. He breathed a sigh of relief when he found the title.
"Here it is right here, 'Mathematics 101 - An Introductory Text.'"
He shot the Chief a questioning look.
Coltrane closed his eyes and shook his head. "I was afraid of that."
The officers were puzzled. "Afraid of what?"
"A text book case," he answered. "We got us a math murderer on our hands."