The Las Vegas massacre last October was not the first time a gunman entered the Mandalay Bay hotel with the intent of gunning down visitors ... this according to new legal docs.

Victims of the October shooting have sued Mandalay Bay, claiming the hotel was negligent by not properly thwarting the attack. The hotel has responded by saying it owed no legal duty to the victims, in part because there was no prior warning or incident that would have put it on notice.

According to docs, there was indeed a "nearly identical situation" 3 years before the October rampage. On November 29, 2014, a housekeeper discovered a guest on the 24th floor had brought multiple semi-automatic assault weapons into his room. One of the weapons was a high-powered rifle equipped with a scope, which was positioned so it pointed out of his hotel room onto the Las Vegas Strip.