Reports indicate that up to four suspicious people were spotted on the roof of a South Melbourne, Australia, hotel the night of January 16, just before an unknown noxious substance was released into the HVAC system of the Wayside Hotel. The mystery irritant, which police believe may have been mace or capsicum spray, apparently was introduced into the hotel environment via the hotel's A/C system around 2 a.m. AEDT.

Roughly 300 people were evacuated from the hotel, and more than a dozen were evaluated by paramedics and some of those were taken to a local hospital for treatment. Hotel patrons complained of headaches, dry throats, nausea, and respiratory problems. Police said the perpetrators could have been attempting to cause mass panic among the patrons.

Local newspapers reported that evidence was discovered on the roof and that witnesses spotted a possible intruder near the roof top entry to the A/C system. The hotel's duct system is being swabbed in an attempt to identify the irritant and provide additional clues.