(CNN) -- Organizers of a "Hunt for Heroes" parade that culminated in a deadly locomotive-and-parade-float collision last week did not apply for a parade permit, officials in Midland, Texas, said Tuesday, raising questions about whether the railroad had been notified of the parade and why city police were serving as escorts.
In a written statement, city spokesman Ryan Stout said, "The city of Midland did not issue a permit nor did the city receive a permit application from the Show of Support organization."
Event sponsors are required to take out $1 million liability insurance policy and to get approval from the police, fire, health departments, according to applications on the city's web site. Sponsors also sign a "right of way use permit" indemnifying the city.
The sponsor of last weeks' event -- a military appreciation group called "Show of Support" -- did not return a phone call from CNN seeking comment Tuesday evening.
Four military veterans were killed and more than a dozen people were injured last Thursday when a large flatbed trailer, serving as a parade float, crossed railroad tracks and was hit by a fast-moving Union Pacific train. The National Transportation Safety Board said the truck entered the railroad crossing as the warning lights and bell activated, and that the gate lowered onto the trailer, knocking down flag poles.
Some people were able to jump from the float before it was broadsided by the train.
Following the accident, the National Transportation Safety Board said its investigation would include a review of the permitting process, and whether those procedures were followed.
"There's a lot of other information that we need to get about the requirements of having a parade, about what notification was given to the railroad, what the specific plan was that the police had for the route, for the activities of the escorts, etc.," NTSB member Mark Rosekind said during a briefing last Saturday. "All of that will be looked into to see exactly what role they might have played in the accident."
The NTSB on Tuesday declined to say whether it had been notified that no permit existed, saying only that it was continuing its investigation.
Stout said members of the Midland Police Department and Midland County Sheriff's Office participated in the parade. "It was volunteer-based. They voluntarily helped with the parade," he said.
"Because this was a reoccurring parade, they decided to help out. They had a presence at the past parades as well."
Asked about why police participated in a parade that did not have a permit, Stout declined to speak further.
On Tuesday, NTSB investigators staged a locomotive and a truck at the accident scene to conduct a "sight distance study."
The test will answer the question: "What could be seen, when, (and) where?" Rosekind said.
An attorney representing Smith Industries, the owner of the truck that served as the float, identified the driver of the truck as Dale Andrew Hayden.
"He's devastated," attorney Doug Fletcher said.
NTSB officials said they are working with the trucking company to arrange an interview with the driver.
Fletcher said Hayden is under a physician's care.
"He is an Army veteran and an active reservist and was honored to be driving his fellow veterans," Fletcher said.
No charges have been filed in the accident.
CNN's Vivian Kuo contributed to this report.