It’s unclear why suspect Dimitrios Pagourtzis was wearing a duster-style trench coat during the shooting rampage at Santa Fe High School on Friday, considering the district’s dress code policy prohibits that type of clothing.

Many school districts changed their clothing policies since the 1999 Columbine High School massacre in Littleton, Colorado. Both gunmen in that mass shooting wore long coats and were investigated for ties to a student group known as “The Trench Coat Mafia.”

Concerns about copycat crimes fueled dress code reforms nationwide. In 2006, 18-year-old Alvaro Castillo was reportedly fixated with Columbine when he opened fire at Orange High School in North Carolina and injured two students.

At Santa Fe High School, officials said Pagourtzis used a duster-style coat to conceal the weapons he allegedly used to kill eight fellow students and two teachers.

“From what we know, this dude walked in today with a long coat and shotgun under his coat,” Texas Lt. Gov. Dan Patrick said Friday. “It’s 90 degrees.”

Several students told KHOU Pagourtzis often wore the same coat to school, the same duster-style coat he posted on Facebook weeks earlier. It was adorned with pins and medallions representing rebellion and evil.

Santa Fe ISD’s student handbook states “trench coats are not acceptable as a form of outwear and will not be accepted at school.”

The ban on the long coats is common in school.

KHOU 11 Investigates checked all 45 school districts in the Harris, Brazoria, Fort Bend, Galveston and Montgomery counties. Twenty of those districts prohibit trench coats district wide. Those include Cypress-Fairbanks ISD, whose superintendent sent a note to parents and students about the ban two days ago.

MAP: Trench coat bans in Houston-area schools

Other school districts have campus-specific dress codes.

In Houston ISD, only three high schools ban trench coats—Madison, Scarborough and Westside.

In Conroe, The Woodlands, Oak Ridge and Caney Creek high schools ban trench coats. Caney Creek’s student handbook states, “Clothing that could conceal any form of weapon from a visual inspection is prohibited.”

Santa Fe ISD would not directly answer questions about the trench coat Pagourtzis was wearing.

District Spokesperson Patti Hanssard provided the following written statement: "Our top priority as we work alongside federal, state and local law enforcement agencies is planning for our students safe return. Dress code is a part of our annual planning and review."