The failure of a Storybook Land ride that derailed earlier this week was not detectable through daily inspections, amusement park owners said Thursday in a written letter.

Independent tests by a company hired by the Egg Harbor Township amusement park have shown that the incident was caused by the failure of an internal steel component. Although the ride could be repaired, the Fricano family, which owns the park, has decided that the ride will be removed at the conclusion of all testing.

The state Department of Community Affairs is investigating the accident. The results of the state investigation have not been released.

The Big Truck Ride derailed Sunday, sending two adults and a child to the hospital for treatment of minor injuries. A cart was about to make a right turn and landed on its right side. The riders fell about two and a half feet to the ground, police said.

Injured were Vineland residents Mary Lorito, 56, and Renee Lorito, 26, and a 1-year-old boy from Pine Hill.

The Big Truck Ride was installed at the park in 1988 and has passed annual state inspections. The ride never has failed any inspection, and the owners were not aware of any issue with the ride component that failed, park officials said.

The May 8 incident was "the first significant mechanical failure of a ride" since the park opened in 1995, the owners said.