Keep Out of the Everfree Forest

After Emerald and Sapphire had breakfast, they set about walking to Sugarcube Corner to check on Mrs. Cake.
As they walked through the town square towards the sweet shop, Emerald looked down the road. She saw a familiar figure a fair distance away, galloping towards them.
“It’s Zecora!” said Emerald happily. “She made it out!”
Sapphire frowned. “She’s in a bit of a hurry, though. Something in the forest must have spooked her.”
The girls waited as Zecora made her way towards them. When she got there, she did something Emerald and Sapphire were not expecting.
Zecora opened her mouth, causing a mouthful of blood to splash onto the ground. The girls gasped as they realized that her tongue had been cut out of her mouth.
The zebra let out a quiet gurgle and collapsed on the ground.
The two mares stood in shock. Busy shoppers dropped their bags as they stared at Zecora on the ground.
A police officer galloped over to Zecora, reaching out to feel her pulse.
“She’s gone,” he said. “Wait…”
The officer noticed a piece of string tied around the corpse’s neck. He gingerly untied it and picked up the note attached to it.
“I told you ponies to keep out of my forest,” he read aloud.
“It was them, officer!” shouted a mare, pointing at Emerald and Sapphire.
“What proof do you have!?” yelled Sapphire unexpectedly. Emerald saw her friend’s eye twitch, and it looked as though it had changed color again; this time to a bright, fluorescent yellow.
Another mare stepped forward. “I saw them leaving the forest not long ago. They killed Zecora!”
The officer stood up. “Girls, come with me.”
The three ponies walked around the corner into a dark alleyway.
“Girls, I don’t have any proof that you did this,” said the police officer. “so I’m going to let you go for now. I suggest you go home and lay low for a while. The townsfolk have you pinned up for two murders already. If this happens a third time, there’s no telling what ponies might do.”
“Got it,” said Emerald.
The officer left them alone in the dark, dirty alley. Emerald and Sapphire immediately made a beeline for the library.
They burst in without knocking, scaring Twilight so much that she shot a bolt of lightning at them, missing them by inches.
“Goodness me, girls,” Twilight said breathlessly. “Don’t do that!”
The two mares took no notice of the dangerous spell.
“Twilight,” Emerald said. “Zecora’s dead.”
“Dear, sweet Celestia,” mumbled Twilight. “Poor Zecora. I’m going to miss her so much.”
“We will too, Twilight,” said Sapphire.
Twilight sadly shook her head. “Well, at least tell me she told you something useful.”
“We figured out two things,” Emerald said. “The killer only attacks ponies who enter the forest. If you stay out, you’re safe.”
“What else?” asked Twilight, brushing away a tear.
“The killer likely lives somewhere in Ponyville,” replied Sapphire.
“So one of the stallions in Ponyville is a murderer, but as long as you don’t go into the forest, you’ll be alright,” Twilight concluded.
“That’s pretty much all we know,” Emerald said.
Twilight wiped her eyes again. “Did Zecora at least die peacefully?”
Emerald uneasily shifted from hoof to hoof.
“For your sake, I won’t go into detail. Let’s just say somepony was sick of her rhymes.”