Philadelphia, PA — Officials are still investigating what caused a carbon monoxide leak that killed one person and sickened several others on Tuesday.

The city has posted a sign along the 4700 block of Chester Avenue declaring an apartment building “unfit for human occupancy”.

It’s been cited by Licenses and Inspections for being in violation due to a carbon monoxide leak.

On Tuesday, 59-year-old Francis Horst, a longtime fixture of the Gables Bed and Breakfast, was found dead on the first floor of the Chester Avenue apartment building.Horst was found by his boss Cesar Gonzales after he didn’t show up to work.

“We have a key to his apartment, and when I opened it, I saw him in his chair, lifeless,” recalled Gonzales.

Gonzalez called 911 and the 40-unit apartment building was evacuated.

Fire officials said two residents went to the hospital complaining of carbon monoxide poisoning symptoms on Monday night.

“I think if I didn’t go there, there could be more casualties,” said Gonzalez.

Action News Troubleshooter Nydia Han asked the building’s manager, Keith Cohen, if the building had working carbon monoxide alarms. He said he had no comment on that, but claimed the building is up to code.

Cohen also said he would now install carbon monoxide detectors on Wednesday and work with his fire alarm company to eventually get them hardwired.

“It’s the holiday season, be careful. And I hope this doesn’t happen to somebody else. Hopefully, this is a wake-up call,” said Gonzalez.

Cohen said PGW did turn the gas off on Tuesday and tagged a heater. He said tenants can stay in the building once the heater is replaced or repaired.

Gonzalez says while Horst’s title was that of gardener and groundskeeper, he was more like an angel.

“He’s such a big loss to this community. He’s been here for 30 years,” he said.

City code does not require buildings of this size to have carbon monoxide alarms, but safety experts warn it is critical that everyone should install them no matter the size of the building.