NORTH BRANFORD, Conn. (AP) — Federal investigators have concluded that a blocked fuel line most likely caused a 2017 plane crash in Connecticut that killed NASCAR driver Ted Christopher and an 81-year-old pilot.

Officials with the National Transportation Safety Board found that a fuel selector valve in the single-engine Mooney M20C plane was clogged by a mass of reddish fibers that appeared to come from red cotton shop towels, according to an NTSB report released Tuesday.

“Disassembly of the fuel selector revealed a piece of red, fibrous material consistent with a shop towel that likely inhibited fuel flow to the engine and resulted in fuel starvation and a total loss of engine power," the report said.

Investigators said improper maintenance allowed pieces of a shop towel to get into the fuel selector.

The plane crashed into trees in North Branford, Connecticut, on Sept. 16, 2017, en route from Plainville, Connecticut, to Westhampton Beach, New York, where the 59-year-old Christopher was to race at a nearby racetrack the same day. The pilot, Charles Dundas, a longtime friend of Christopher's, also died.

During his career, Christopher had 131 wins, 109 SK Modified wins and nine SK Modified track championships.