The US military insists that that the recovered material was a top-secret research balloon, however many UFO theorists believe that the wreckage was of from a crashed alien spacecraft and that the military covered up its recovery.
On 8th of July 1947, William "Mac" Brazel, foreman of the Foster Ranch, and Dee Proctor found the crash site on the Foster ranch 75 miles north of Roswell, where they were presented with a field containing vast quantities of what appeared to be tin foil. Some of these foil-like pieces were easily crumpled by hand, and which completely recovered their original shape, showing no signs of wrinkling when released (memory metal anyone?), while other pieces could not be deformed or damaged by any means, even when struck with a sledgehammer.
Because of the material's unusual properties, Brazel took pieces of the debris to the authorities in Roswell. Intrigued by the debris, Colonel Blanchard, commanding officer at Roswell Army Air Field, ordered two intelligence officers to investigate. Upon their report, Colonel Blanchard quietly ordered that the ranch area be cordoned off. Within the hour the place was swarming with Army officers, who promptly sealed off the area from all civilians. The place was swept with a fine comb so as to leave no trace of the wreckage.
Roswell Army Air Field (RAAF) issued a press release stating that personnel from the field's 509th Bomb Group had recovered a crashed "flying disc" from a ranch near Roswell, which sparked intense media interest. During the war, the 509th Bomb Group was tasked with developing and employing a combat delivery system for the Atomic bomb and conducted the attacks on Hiroshima and Nagasaki, Japan, in August 1945. Coincidence?.
Later, on that same day, the Commanding General of the Eighth Air Force stated that, in fact, a weather balloon had been recovered by RAAF personnel, rather than a "flying saucer." A subsequent press conference was called, featuring debris said to be from the crashed object that seemed to confirm the weather balloon description. Public interest faded, and the Roswell incident became a memory, with most people accepting the official story.
It wasn't until much later, in 1978, when ufologist Stanton Friedman interviewed Major Jesse Marcel, who was one of the two intelligence officers initially involved with the recovery of the debris. Marcel expressed his belief that the military had covered up the recovery of an alien spacecraft. In February 1980, The National Enquirer ran its own interview with Marcel, gaining national and worldwide attention for the Roswell incident.
Additional witnesses and reports emerged over the following years. They added significant new details, including claims of a large military operation dedicated to recovering alien craft and aliens themselves, as many as 11 crash sites, and alleged witness intimidation. In 1989, former mortician Glenn Dennis put forth a detailed personal account, wherein he claimed that Roswell alien autopsies were carried out at the Roswell base. Out of the hundreds of witnesses that were interviewed by the various researchers, but only a few were found to be true witnesses. The majority were repeating the claims of others.
Skeptics all agree that something crashed near Roswell in 1947, but not an alien craft. Alternative explanations vary from weather balloons to secret aircraft to espionage devices. It is currently believed that the wreckage was part of Project Mogul, a top secret project testing giant, high-flying balloons to detect Soviet nuclear explosions.