Swansea, Illinois, police did not name Busch as the pilot, but he is identified in a search warrant application. St. Clair County State's Attorney Brendan Kelly said his office is awaiting toxicology results before deciding whether to file charges.
Busch's attorney, Maurice Graham, was out of the country Tuesday and did not immediately respond to messages seeking comment.
Busch, 53, was chief executive officer of the St. Louis-based beer maker from 2006 until it was bought out by InBev in 2008. He is the great-great-grandson of Adolphus Busch, the founder of Anheuser-Busch.
Swansea police said in a news release that a helicopter landed in an office park close to buildings at 12:48 p.m. Monday. The pilot was gone by the time officers arrived. No injuries were reported.
A caller at 8:14 p.m. Monday told police the pilot had returned "and appeared too intoxicated to take off," the police news release said. An arriving officer found that the "helicopter rotors were spinning and the engine was revving up."
When the officer turned on emergency lights of her car the pilot powered down the engine.
The search warrant application said a breathalyzer did not indicate alcohol intoxication. But the document said Busch was unable to follow directions and acted erratically. His wife told officers that he was off of anxiety medication because of recent fertility treatments.
Officers believed that Busch was under the influence of a controlled substance. He was taken to a hospital for further testing.
The application said Busch told officers he had a conceal carry license and had a gun in his pocket, along with the prescription drug Dexamethasone. Police said the prescription was for his wife.
Officers found three other loaded guns while searching the helicopter, along with several other bottles of prescription drugs.
The document said Busch told officers at one point that he was about to have a panic attack, and he began jumping and running while saying he needed more oxygen to "cope with the anxiety attack."
Busch, who has a commercial pilot's license, spent the night in custody before being released Tuesday afternoon. The helicopter was still parked at the office complex.
Police Chief Steve Johnson said his office was in communication with the Federal Aviation Administration about the incident.
"This is not your normal case that a street police officer handles. The safety and security of the community, the pilot and passenger were of the utmost concern," Johnson said in the release.
Busch was in college in 1983 when he was involved in a car crash in Arizona that killed a 22-year-old woman. He was not criminally charged.
In 2010, his girlfriend, Adrienne Martin, 27, died of an accidental drug overdose at his estate in the posh St. Louis County town of Huntleigh. He paid $1.75 million in 2012 to settle a wrongful-death lawsuit.
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