Investigators found no initial evidence of tampering on Barack Obama's campaign plane, which was forced to make an unscheduled stop earlier this week after an emergency slide deployed in flight.

The National Transportation Safety Board released an update Thursday finding that the evacuation slide in the tail cone of the plane was partially inflated and that it had "marks consistent with rubbing of elevator control cables."

But the report said an inspection of the hardware "did not reveal any evidence of missing components, nor any evidence of tampering."

The plane, a Midwest Airlines flight, set down in St. Louis shortly after taking off from Chicago Monday en route to Charlotte, N.C., where the presumptive Democratic presidential nominee was supposed to give an address on the economy. The early landing was not classified as an emergency.

The preliminary NTSB report said the slide's inflation bottle was empty and noted some irregularities with the elevator cables. The report said a catwalk railing was broken and "impinged upon elevator control cables." The flight crew told investigators that, while they did not hear the slide deploy, they noticed "elevator control stiffness" shortly after departing from Chicago.

The safety board has removed the slide and hardware, as well as flight recorders and maintenance records, for further analysis.