There are 3D printers which use lasers to cure photo-reactive resins; this SLA (StereoLithographyApparatus) process was the first 3D printing process, patented in 1986 by Chuck Hull, who went on to found 3D Systems Corp. There are several prosumer-level machines on the market that use this method to build parts. It's hard to imagine a scenario in which a machine like that could emit enough toxic gas to kill two people and their cats, though - these are tiny lasers, not the kind that can cut things or burn them.


But, reading the reports, while it doesn't seem like there really was a 3D printer at the scene of this tragedy, there may have been a laser cutter. Those machines have more powerful lasers, and can burn through organic materials like leather, thin wood, and plastics. There are certain plastics which, when burned, can emit toxic fumes. Urethanes, for example, put out isocyanates as a product of combustion. Those were responsible for the disaster at Bhopal, and continue to claim new victims: https://www.cdc.gov/niosh/topics/isocyanates/


If these folks were experimenting with an unventilated laser cutter at home, maybe trying to cut some urethane foam, then this tragedy might not be totally inexplicable.