The murder charges against the designers and owners of a water slide that decapitated a 10-year-old boy in the US have been dropped.

Caleb Schwab was killed on the 170-foot-tall Verruckt water slide at Kansas City’s Schlitterbahn Waterpark after the raft he was on went airborne and his head struck a pole.

Following Caleb’s death, state attorneys brought criminal charges against operators and associates of the water park, accusing them of recklessness.

But on Friday, a judge dismissed the charges and said prosecutors had submitted “improper evidence”.

In his ruling, Judge Robert Burns of Wyandotte County wrote that there was “illegal evidence that should not have been presented to the grand jury” and called into question videos and expert testimony presented to jurors.

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The slide, known as Verrückt, which is German for “crazy” or “insane”, opened in 2014 and was marketed as the tallest water slide in the world.

Riders climbed 264 steps to the top before sitting in a raft that plummeted and then soared over a crest on its way to a runoff pool at the bottom.

The rafts sometimes lifted from the chute momentarily, and the slide was covered with netting, supported by metal poles, so riders would not fall off.

But riders sometimes struck the netting or the poles, and some injuries had already occurred when, in August 2016, Caleb Schwab, 10, got into a raft with two other riders.

As his raft soared over the crest, Caleb was tossed towards the netting. He hit a metal pole and was decapitated.

Tallest waterslide in the world

In 2017, Caleb’s family received a settlement of nearly $20m from Schlitterbahn and other companies involved in the slide, the Kansas City Star reported.

Caleb was the son of Scott Schwab, a former Republican state senator who recently took office as Kansas secretary of state. The two women in Caleb’s raft — sisters who suffered facial injuries and bone fractures — also received settlements from the park.

Criminal indictments came in 2018. The defendants included Jeffrey W Henry, a co-owner of Schlitterbahn Waterparks and Resorts, which is based in Texas; John T Schooley, a designer of the slide; and Tyler Austin Miles, a former operations director. Also indicted were Henry & Sons Construction Co and KC Waterpark Management, both affiliates of Schlitterbahn.

They were accused of reckless behaviour in the design, construction and operation of the Verrückt and faced various charges that included aggravated child endangerment and second-degree murder.

In seeking the indictment, state attorneys showed grand jurors video footage filmed for a Travel Channel show, “Xtreme Waterparks”, which featured the slide in an episode. The video was intended to show that the defendants had exhibited a reckless attitude towards the construction of the slide, Mr Burns wrote.

“The video, though, is a fictional and dramatised version of events created for entertainment purposes”, he wrote, concluding that it should not have been allowed as evidence.

Burns also wrote that the jurors heard expert testimony that suggested, incorrectly, that the slide’s designers did not adhere to legal standards, and that the expert mentioned another, unrelated death at the Schlitterbahn park in Texas.

Ultimately, he decided that the defence lawyers’ arguments of “grand jury abuse” were credible.

“I obviously recognise that the circumstances and events giving rise to these indictments are indisputably tragic,” Mr Burns wrote. “A young child’s life was lost and his troubling death was mourned by family, friends and the entire Kansas community and beyond.”

Winter Prosapio, a spokesperson for Schlitterbahn, said the company welcomed the decision. “We are thankful for all the support and encouragement we’ve received,” she added.

“We agree with the court’s decision that the grand jury was not given a fair picture of the evidence relating to this tragic accident,” Justin Johnston, a lawyer for Mr Schooley, said. “We don’t know what the future holds, but hope that with a fresh look at the evidence and law, the parties can find a way to put this matter behind them.”

Tricia Bath, a lawyer for Mr Miles, said “there is no question that Friday’s ruling about what occurred before the grand jury was correct and the judge’s reasoning legally sound.”

Lawyers for the other defendants either could not be reached on Saturday or did not immediately respond to requests for comment.

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In a statement, Kansas Attorney General Derek Schmidt did not rule out seeking criminal charges again.

“We are obviously disappointed and respectfully disagree with the court’s decision,” the statement said, adding that prosecutors would “take a fresh look at the evidence and applicable law in this tragic and troubling case to determine the best course forward”.

A lawyer who represented the Schwab family did not immediately respond to a request for comment on Saturday.

The Verrückt water slide was demolished last year.