The Junior Crime Solvers Club - The Case of the Scorned Mistress

"You see how the machete wounds are so deep in the neck that it nearly severed her head?" Billy asked.
"I guess so," replied Fatty nervously.
"And how her vagina is split all the way up to her sternum?"
" But what does that mean?"
"Duuuh," sneered Janey, popping her gum. "It's obvious that the killer was very angry with her about something. That's why there was such brutality in the murder."
"That's right, Janey," agreed Billy. "Whoever our killer is must have been very close to Ms. Jennings. Chinky, how did the DNA test on the discarded condom we found turn out?"
"Inconcrusive." Chinky reported.
"We've got to wrap this one up soon guys," Fatty said. "I've got to be home for dinner by six."
Just then, Billy saw a major clue that they somehow all missed when they examined Ms. Jennings' mangled corpse. "Fatty," Billy said confidently, "I have a feeling that you'll be home for dinner even earlier than usual this time!"
Twenty minutes later, the gang of young detectives had everyone in town gathered around the bloody crime scene. "All right kids, now what's this all about?" asked Police Chief Taggart.
"We have solved the case of the scorned mistress!" Janey announced.
"Oh have you now?" Chief Taggart chuckled. "And just what have you come up with?"
Billy addressed the assembled townsfolk gravely. "The murderer of Ms. Jennings is......Chief Taggart!"
The crowd let out a great gasp. Police Chief Taggart turned bright red and began to stammer. "That's ridiculous!" he thundered. "What is your proof?"
Billy held up a small plastic bag that everyone strained to see. "Well Chief, you almost got away with the perfect crime, but you forgot one tiny little detail..."

What was the smoking gun that lead to Chief Taggart? Will the Junior Crime Solvers Club pursue the death penalty? Find out next week!