The 38-year-old man's statement is contained in a Wayne County airport police report obtained by The Associated Press via a Freedom of Information Act request.
An X-ray operator for the Transportation Security Administration noticed the knife during an initial screening July 6 at Detroit Metropolitan Airport in Romulus, the report said. She then asked for a colleague to check the man's bag.
That TSA screener said in a written statement that he discovered the "artfully concealed knife" in the lining of the left shoe. The passenger said "he was told that if he put the knife under the insole that it would not be seen on the X-ray," the TSA agent wrote.
The man told police the stainless steel Kershaw folding knife, similarly concealed, had not been "discovered or confiscated by the TSA" at the airport in Huntsville, Alabama, three days earlier.
As a result, police said, the man said he "did not think it was a criminal violation of law to have the knife in his luggage."
The suspect, who is from Alabama, had gone fishing at property owned by his grandfather in Clare, Michigan, and was returning home on a Sunday morning when he was stopped at Detroit Metro's North Terminal. The man was handcuffed, arrested on a checkpoint violation and placed in a holding cell, according to the report.
Airport spokesman Brian Lassaline said the man was released while prosecutors decide whether to charge him, Maria Miller, a spokeswoman for the Wayne County prosecutor's office, said Friday he has not been charged.
The TSA has said the knife should have been placed in checked luggage.