Updated

Iowa's biggest newspaper is under fire after publishing a map that showed which public school districts have police or security -- and which ones don't.

Critics said the Des Moines Register, which quickly pulled the interactive map off of its website, was making it easy for a deranged killer to know where to launch a Sandy Hook-style attack.

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"What they did yesterday was provide a shopping list for every nut job in Iowa," WHO radio host Simon Conway, who said his phone lines "blew up" as soon as he began discussing the map with his audience, told Fox News Channel.

The paper's investigation, which Editor Rick Green said was mounted in response to the Dec. 14 attack in Newtown, Conn., which left 20 children dead, found hundreds of schools have no police or private security during portions of the day. Of the state’s 25 largest school districts, only three do not utilize school resource officers, a survey by the by Des Moines Register newspaper found. The online map that originally accompanied the story allowed readers to identify more than 100 public schools, including high schools and community college campuses with varying degrees of security.

Green told Fox News Channel that the map was only on the paper's website for 20 minutes, after which it was taken down amid an avalanche of angry phone calls.

"My team alerted me to it, and we took it down," Green said.

Green said the paper wanted to show how security resources were being deployed across the state, but later changed to a map that showed the 54 districts that have full-time security. But some law enforcement and school authorities in the state said that the number of officers in the schools could increase as officials continue to update security plans.

“This was a deliberate decision” at Linn-Mar’s school system, Superintendent Katie Mulholland wrote in response to the Register’s survey. “However, the Marion Police Department makes rounds in our school buildings on a regular but varied schedule, about every five days where they walk the building and their squad cars are visible in the school parking lots.”

Most districts shared the cost of the resource officers with a local law enforcement agency, the newspaper found.

Green acknowledged that he wished the map had been presented differently, but said it was meant to be a "revelatory look" at an issue that concerns parents and taxpayers.

"When taxpayers and residents are calling us to inquire about how safe their children's schools are, we have to investigate," Green said.

Click for more from the Des Moines Register.