From the names of the victims, it could be.
But that’s not that ‘mysterious’, authorities should be able to determine the cause fairly quickly.
Esp. if there are plenty of evidence that they were in the process of cleaning, and with buckets of both agents on hand close by.
HCl (chlorine stripping hydrogen from water) causes burns and hemorrhaging of mucosa and lung tissue. Persons exposed get a whiff and run if that option is available. Enough chlorine to quickly incapacitate persons inside a structure would linger and be evident to responders.