Another photo shows the girl in suspenders, who had fake blood on her shirt, sitting in a car. The caption underneath the image reads, “Bang bang, brother.”
Pamela Stephens, superintendent of Adair County Schools, announced the girls' suspension in a statement, WHAS reported.
“We take the situation very seriously, and our personnel are continuing to investigate the facts and circumstances surrounding this matter,” Stephens said.
The length of the girls’ suspension was unknown.
Some parents were angry that the costumes garnered only a suspension. One mother, Amy Tarter, told WHAS that the punishment was "ridiculous."
"I think any child that does that should be expelled, and any parents who (support) their child (doing that) should have charges brought against them," Tarter told the news station. "You worry every day about sending your kid to school, and now you have people joking about it."
The girls' Halloween costumes are not the only ones stoking ire this year. A man in Owensboro, Kentucky, found himself apologizing after dressing his 5-year-old son as Adolf Hitler last month for a city event. The man, Bryant Goldbach, dressed as a Nazi officer.
A nurse in Missouri lost her job earlier this week for dressing in blackface as Beyonce -- with her husband dressed in blackface as Jay-Z -- and a man in Picayune, Mississippi, was kicked out of a bar Saturday for showing up for a costume contest in a Ku Klux Klan robe.
The Columbine school shooting, which also left 21 students and teachers wounded, was the worst in U.S. history when it occurred in 1999. It has since been eclipsed by multiple school shootings, most recently the shooting at Marjory Stoneman Douglas High School in Parkland, Florida, on Valentine's Day. Former student Nikolas Cruz, who is awaiting trial, killed 17 people and injured 17 more before fleeing the campus and being caught by police.
A total of 14 people were killed at the University of Texas in Austin on Aug. 1, 1966, when student and former U.S. Marine Charles Whitman began shooting from the campus' iconic clock tower. More than 30 people were also injured before Whitman, who killed his wife and mother the night before, was shot and killed by police officers.
The Sandy Hook Elementary School shooting on Dec. 14, 2012, is the second-worst in U.S. history, with gunman Adam Lanza leaving 26 children and teachers dead before killing himself. Lanza killed his mother, Nancy Lanza, before going to the school in Newtown, Connecticut.
The worst school shooting in America was the April 16, 2007, shooting at Virginia Tech, which killed 32 people and injured about 30 more. The gunman, student Seung-Hui Cho, fatally shot himself when he was done.
The worst school massacre in American history was not a shooting, but an explosion that killed 44 people -- 38 of them children -- at the Bath Consolidated School in Bath Township, Michigan, on May 18, 1927. The perpetrator, school board member Andrew Kehoe, killed his wife, Nellie, at their farm prior to setting the explosives at the school.
In the aftermath of the explosion, Kehoe detonated explosives he had in his truck, killing himself, the school superintendent and several other people.