Kansas City - A Kansas waterslide billed as the world's tallest remained off-limits as authorities pressed to figure out how a state lawmaker's 10-year-old son died of a neck injury while riding it.Details remained murky about what happened on Sunday to Caleb Thomas Schwab on the 51m-tall "Verruckt" — German for "insane" - that since its debut two years ago has been the top draw at Schlitterbahn Waterpark in Kansas City, Kansas.Kansas police issued a statement saying that Caleb suffered a fatal neck injury around 14:30 while he was riding the slide with two women, neither of whom was related to him. They suffered minor facial injuries and were treated at an area hospital.Emergency responders arrived to find the boy dead in a pool at the end of the ride, according to the statement, which offered no further details.In a statement on Monday afternoon, Schlitterbahn said it was "deeply and intensely saddened for the Schwab family and all who were impacted by the tragic accident". The park was tentatively scheduled to reopen on Wednesday, but "Verruckt is closed", according to the statement.Civil matterOfficer Cameron Morgan, a police spokesperson, said no police report about the incident was available. He said investigators were treating Caleb's death as a "civil matter" rather than a criminal one and referred additional questions to the park.Leslie Castaneda, who was at Schlitterbahn on Sunday, said she saw Caleb's crumpled shorts or bathing suit at the bottom of the ride, along with blood on the slide's white descending flume."I'm really having a tough time with it. I really am," said Castaneda. "I saw his [Caleb's] brother. He was screaming."On the waterslide certified by Guinness World Records as the world's tallest, riders sit in multi-person rafts during "the ultimate in water slide thrills," subjecting "adventure seekers" to a "jaw dropping" 17-storey drop, the park's website says. Passengers then are "blasted back up a second massive hill and then sent down yet another gut wrenching 15m drop," the website adds.Each rider must be at least 1.4m tall, and the group's weight is limited to a total of 181- to 226 kg. Authorities didn't release information about Caleb's height or the combined weight of his group of riders.In a news article linked to the news release announcing a 2014 delay, Schlitterbahn co-owner Jeff Henry told USA Today that he and senior designer John Schooley had based their calculations when designing the slide on roller coasters, but that didn't translate well to a waterslide like Verruckt.In early tests, rafts carrying sandbags flew off the slide, prompting engineers to tear down half of the ride and reconfigure some angles at a cost of $1m, Henry said.A promotional video about building the slide includes footage of two men riding a raft down a half-size test model and going slightly airborne as it crests the top of the first big hill.Prosapio said on Sunday the park's rides are inspected daily and by an "outside party" before the start of each season.