Colonel Charles A. Lindbergh was an American hero. On May 20, 1927, the Lone Eagle, as he was known, became the first person to fly solo across the Atlantic in his single-engine airplane, the Spirit of St. Louis. Less than five years later, on the night of March 1, 1932, his son, Charles, Jr., was abducted from the second-floor nursery of his Hopewell, New Jersey, home.
Clues were meager. A ransom note was left on the nursery windowsill, and a ladder lay on the ground beneath the window. Dusting the ransom note envelope revealed no latent fingerprints, but analysis of the writing led investigators to believe that the writer was poorly educated and likely of German descent. The ladder was homemade, suggesting that the kidnapper had tools and was skilled in carpentry.
As the case progressed, communications began between the kidnapper and John F. Condon, a public school principal who had publicly offered a reward for the return of the child. Condon turned over a $50,000 ransom in exchange for a note stating that the child could be found near Martha's Vineyard Island onboard a boat named Nelly. Unfortunately, no such boat existed, and on May 12, 1932, the decomposing body of the child turned up in a wooded area near Lindbergh's home. The cause of death was either asphyxiation or blunt-force head trauma.
Police had recorded all the serial numbers of the bills used for ransom, and during the next 2-1/2 years, the money occasionally surfaced between New York and Chicago, with a higher concentration of it turning up in the Bronx.
As the investigators' attention turned to the ladder, Arthur Koehler, an expert in wood and wood products, was brought in on the case. During his examination of the ladder, he found that four different types of wood were used in its construction: ponderosa pine, North Carolina pine, birch, and fir. The fir appeared to be a section of flooring that had been used to finish the left upper part of one of the ladder's rails and indicated the builder of the ladder had run out of wood and used a piece of flooring to complete the construction.
Koehler microscopically examined portions of the ladder and discovered marks that suggested that a planing machine had been used to smooth the side rails. He discovered several distinctive marks on the wood that had been made by the machine. Koehler asked for planed wood samples from more than 1,500 mills across the country and discovered the same marks on wood milled by Dorn Lumber in McCormick, South Carolina. From there, he traced the wood used in the ladder to National Lumber and Mill Work Company in the Bronx, where much of the ransom money had turned up.
Meanwhile, a service-station operator wrote down the license plate number from the vehicle of a suspicious-looking man from whom he had taken a ten-dollar bill and called the police. The bill, it turns out, was part of the ransom money, and Bruno Richard Hauptmann, a carpenter of German descent, was arrested.
In the attic of Hauptmann's home, investigators discovered a floorboard missing from a joist that had four nail holes that exactly matched holes found in the piece of fir used to finish the ladder. Koehler also found a handheld wood plane in Hauptmann's home that sported defects that matched distinctive marks left on certain areas of the ladder during the smoothing process.
Koehler then applied a well-known trick of the forensics trade. He wrapped a piece of paper around the wood from the ladder and rubbed a pencil back and forth until a black-and-white replica of the pattern left by the wood plane appeared. He later applied the same technique to another piece of wood that he'd smoothed with the same plane. They matched.
Based on the evidence provided by Koehler and the fact that some of the ransom money turned up in Hauptmann's garage, Hauptmann was convicted of the kidnapping and murder of Charles Lindbergh, Jr., on February 13, 1935. He was executed April 3 of the same year.