The Federal Bureau of Investigation (FBI) investigated hundreds of UFO sightings in the 1940s and '50s, but the agency had a policy of destroying investigation records because they took up too much space.

Some of the papers related to these UFO sightings went online this weekend through the FBI's newly revamped electronic reading room, dubbed The Vault. Previously known as the FBI Records/Freedom of Information and Privacy Act website, the site contains more than 2,000 FBI documents that were scanned from the original paper files. Many of these documents are available to the public for the first time.
One section of the Vault is reserved for documents related to UFO sightings. Among the files, reports the Guardian, is a 1949 memo to FBI Director J. Edgar Hoover describes the policy of the Bureau's San Antonio office to destroy files related to UFO investigations because they contained "nothing of interest to the FBI" and were too plentiful to store. "It is pointed out that the filing of these would result in the rapid accumulation of very bulky files," the unsigned memo says.
A memo from 1950 details an investigation of three "flying saucers" that a witness claimed crash-landed in New Mexico, an incident unrelated to the 1947 event in Roswell, N.M., that spawned conspiracy theories about an alien crash. In the 1950 memo, special agent Guy Hottel repeats an Air Force investigator's report that three flying saucers crashed and were recovered, along with the bodies of nine alien crew members. According to the memo, each ship "was occupied by three bodies of human shape but only three feet tall, dressed in metallic cloth of a very fine texture. Each body was bandaged in a manner similar to the blackout suits used by speed flyers and test pilots."
The investigation ended there, and the memo concludes with the statement "No further evaluation was attempted." The informant's name is redacted in the file.
But the memo doesn't tell the whole story. According to the International Business Times, the "Hottel memo," which was never classified, repeats a hoax first reported in a Kansas City newspaper. The two con men responsible were later convicted of fraud.
But speaking of Roswell, another document makes it clear that the 1947 crash was, indeed, a weather balloon, although its exact origin remains uncertain. ABC News cites a 1947 memo with the word "Roswell" handwritten on the top of the page detailing the discovery of a "flying disc" near the New Mexico town. "The disc is hexagonal in shape and was suspended from a balloon by cable. The object found resembles a high-altitude weather balloon with a radar reflector."
The new version of the Vault has been heavily enhanced for online searching and viewing of documents on the Web. It also contains documents related to mobster Al Capone, actress Marilyn Monroe, rapper Notorious B.I.G. and the Sept. 11, 2001, hijackers. The FBI says additional documents will be added every month.