State investigators continue searching for the cause of the train derailment at the Louisville Zoo. One child, a 21 month-old, remains in serious condition.

Investigators spent Tuesday taking pictures, examining the scene and conducting interviews. The Department of Agriculture said the operator of the train was 18 years old. That is the minimum age for an operator in the state of Kentucky.

The train began operating in 2000. State officials said it passed all recent inspections. The last inspection was January 22, 2009. “State law in 2008 also requires the ride operator to inspect and test the ride everyday before its open to the public,” according to one official.

The train is still on its side, detached from its wheels, with wires and mechanics exposed as inspectors try and figure out how and why it jumped the tracks.

Passengers riding the train have their own ideas about what happened. “It started going a little fast through the tunnel and went around some curves and kept gaining speed, and they said the brakes went out, and then it just fell over,” victim Darren Bamforth said.

“We are going to do a thorough investigation. No matter how much time it takes to get to the bottom of what happened and why it happened,” said Ted Sloan of the Kentucky Department of Agriculture.

Zoo officials said the train has a 35 point inspection everyday by the driver. The train is also inspected weekly by the Louisville Zoo maintenance staff.