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A man in Nebraska managed to scale an airport fence, strip down to his boxer shorts, steal a pickup truck and crash it into the nose of an airliner, officials and eyewitnesses said.

Authorities are now investigating how the suspect allegedly managed to get onto the runway of Omaha's Eppley International Airport on Thursday night and ram the Southwest Airlines aircraft at high speed.

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Tim Conahan, chief of police at the Omaha Airport Authority, said the suspect's behavior possibly indicated "some type of drug overdose or that he has mental issues."

A Southwest Airlines jet sits on the tarmac of Eppley International Airport, in Omaha, after a suspect alleged crashed a pickup truck into the jet. David Postier / Twitter

Conahan said that an officer first noticed the suspect " acting in a bizarre manner" and saying "someone was trying to kill him" at around 9:30 p.m. local time (10:30 p.m. ET).

The man bolted through a parking garage and into bushes on the perimeter of the airport — before scaling a barbed-wire fence — according to the officer.

He then found a pickup truck owned by Southwest Airlines that had its engine running and climbed in. After police cut him off as he was going under a jet bridge used to board the aircraft, the suspect crashed the truck into the plane's nosecone, Conahan said.

The aircraft was about to take off for Denver and had 18 passengers on board at the time, according to a statement from Southwest Airlines.

Passengers Beth and Tom Lantry — who were flying to Denver — said they felt "a big jolt." David Postier, a 23-year-old from Littleton, Colorado, said he heard a "loud boom and crash."

Police said the pilot suffered a slight knee injury and a flight attendant bumped an elbow.

The suspect was taken into police custody, according to the airline's statement. Police chief Conahan said the FBI had been notified and the NTSB were also flying out Friday to investigate.