DAYTONA BEACH, Fla. -- A beachside roller coaster derailment that injured nine people last month was caused by "excessive speed," the Florida Department of Agriculture said Tuesday.

Inspectors also found evidence that the Sand Blaster roller coaster had derailed before.

Nine people were hurt when the Daytona Beach Boardwalk coaster derailed June 14. Two of those people were knocked out of the ride vehicle and fell 34 feet.

The agency's preliminary investigation found no mechanical, structural or electrical defects, hence the conclusion that speed caused the crash.

This was also the conclusion of an independent engineer hired to evaluate the ride, who said, according to the preliminary report, that there was no obvious visual deficiency.

Previous derailment evidence found

When the engineer dismantled some of the support structure as part of the investigation, they said there was evidence of a previous derailment in the same area.

The state says the evidence shows the ride had derailed after it was refurbished and initially permitted in 2013, the year the ride opened.

The state's preliminary report says there is evidence of other possible derailments before that. 

"Evidence on the track at the location of the fresh gouge marks conclusively demonstrated repetitive and long-term evidence that the basic accident events had happened many times before," the engineer's report said.

The report speculates that the old gouge marks had been painted over before. The report also says an accident brake fin had evidence of "significant prior damage requiring part of the fin to be removed."

The roller coaster, according to the engineer's report, was first erected in the early 1970s somewhere in the Northeast, before being refurbished and brought to Daytona Beach.

However, the state says no derailments were reported in the agency's reports. The report says whoever signed the ride's affidavit of Compliance and Nondestructive Testing should have known the ride could have posed a serious risk of injury to patrons.

The Department of Agriculture and Consumer Services, which handles attractions inspections, says it has issued subpoenas to get the ride operator to provide additional records.

The agency is also continuing to investigate factors such as weight, weather and track lubrication.

The Sand Blaster remains closed indefinitely.