NEW YORK (CBSNewYork) — There is new information about what went wrong in Sunday’s deadly high-rise fire in the Bronx and the safety failures at the center of the investigation.

An FDNY source told CBS2 there were several space heaters inside the apartment where the fire started, and one of those heaters was reportedly left on for days.

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CBS2’s Jenna DeAngelis also learned federal safety regulators are looking into the heater that sparked the fire. They’re trying to determine if it was defective.

The FDNY is focusing its investigation on self-closing doors inside of the building that may have malfunctioned, allowing smoke to spread.

The death toll was adjusted Monday to 17 people, including eight children. That’s down from the 19 deaths initially reported. Fifteen others remain in critical condition.

Watch: Mayor Adams, FDNY Commissioner Nigro On Deadly Bronx Fire

While there are still questions that need to be answered, one thing that is certain is many people are mourning the loss of loved ones.

“I see smoke. People start calling, people screaming,” said Mohamed Kamara, a relative of one of the victims.

Kamara was standing on the sidewalk on Sunday when he saw the smoke shooting out of the apartment building on East 181st Street in the Fordham Heights section of the borough. He said his first thought was his relatives inside.

“That exact time I know these people are home. I was calling their numbers, no way,” Kamara said.

He said his cousin, his wife and their three children all passed away.

“I feel bad. I can’t sleep. I don’t know what to do,” Kamara said.

Many are still a loss for words trying to figure out what happened.

“I did not sleep. I was crying in my sleep. I was shaking,” building tenant Tysena Jacobs said.

Jacobs was trying to get back inside to get her medication. The sight of broken-out windows served as a reminder of how things could have been worse.

“Maybe we would have died in there with that smoke. It was really, really bad. I couldn’t take it. I dropped on my knees and prayed to God … ‘God, please help us,'” Jacobs said.

The FDNY said the fire was caused by a faulty heater in the bedroom of a second-floor duplex apartment. As the residents raced out, officials say their apartment door should have closed but didn’t, allowing smoke to spread through the building, turning stairwells into a deathtrap.

Mayor Eric Adams said he is doubling down on public service announcements citywide to remind everyone to shut the door behind them in an emergency.

“This painful moment can turn into a purposeful moment, as we send the right message of something as simple as closing the door,” Adams said.

The FDNY said two doors were open inside the building. How that happened remains under investigation.

A spokesperson for the building owner said, “All doors in the building are self-closing, including stairwell and apartment doors, as required. There are no open violations or complaints related to self-closing doors at the property.”

“There has been some stories that the alarm system went off regularly. There’s been some stories that people smoking in the halls set off the alarm. So our investigation will determine that,” FDNY Commissioner Daniel Nigro said.

Meanwhile, the Adams and Schools Chancellor David Banks visited schools grieving the loss of their students. Eight didn’t make it.

READ MORE: Red Cross Helping Families Displaced By Deadly Bronx Fire, Borough Leaders Set Up Task Force To Assist Survivors

“They’re not just a name. They told us stories about each one of them. And my heart broke, as we heard, just about how passionate each young person was and how they came to life for us,” Banks said.

The chancellor said he sent letters to all school principals to make sure they reflect on this tragedy, but also make sure to talk about fire safety in school.

The mayor said President Joe Biden also called Monday to offer his support.

“He has made it clear that whatever we need, the White House is going to be there for us,” Adams said. “He has just sent a very strong message that this is on the radar of the entire globe of what has happened here.”

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Now, the focus is on raising money for the victims and reminding people about fire safety. A cleaning crew spent Monday morning wiping away the mess from the tragic fire, but could never remove the painful memories.

“We pray to God that they are able to pull through. But we know that this has impacted the lives of so many,” Adams said.

As the community mourns and searches for answers, Timothy Cardinal Dolan stopped by the scene Monday to offer his prayers.

“Jesus said fear is useless, what is needed is trust,” he said. “We trust in our fire department. We trust in our experts. And we trust in the Lord. We will get through.”

READ MOREIn Wake Of Deadly Bronx Blaze, FDNY Offers Safety Guidance To Residents Living In Fireproof And Non-Fireproof Buildings

When it comes to fire safety, experts say anyone living in an apartment building should know whether it is combustible. If it is, you should run out as soon as possible if there is a fire.

“If the building is non-combustible, fireproof, and the fire is not in your apartment, you stay in your apartment,” NY Fire Safety Consultants president Jim Bullock said. “You try to keep any smoke from coming into your apartment by putting towels by the door… If you leave that apartment, you go out into a hallway and a stairway that is full of toxic smoke.”

“We do recommend in high-rise fireproof buildings that people should shelter in place and it’s safer to be in your apartment then to venture out and try to get down the stairs,” Nigro added.

Congressman Ritchie Torres described what he saw after touring the apartment where the fire started.

“One of the most horrifying scenes I’ve ever seen,” Torres said.

He said even though there were reports of heat in the building, often inadequate heat and hot water leads to tenants resorting to space heaters.

“Even if the landlord was requiring the legal minimum, what the law requires often falls short of what tenants need to remain warm in their apartments,” Torres said.

That’s something a new task force will focus on as it explores fire safety nationwide.

“My colleagues and I at every level of government — federal, state and local — were coming together to form a legislative task force on fire safety,” Torres said. “We’re looking to examine what policies can we put in place to ensure that there’s fire safety in every residential home, not only in the Bronx but throughout the country. We’re going to examine issues relating to heat and hot water, the manufacturing of space heaters, the use of space heaters in apartments, sprinkler systems, smoke alarms and fire alarm systems, self-closing doors … ”

“We owe it to the lives lost to ensure that their death is not in vain. We have an obligation to make the lessons learned from present and past tragedy into laws that will save people’s lives in the future,” he added.

The mayor has ordered flags across the city to be flown at half staff until sunset Wednesday.

CLICK HERE if you or a loved one was impacted

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CBS2’s Kevin Rincon and John Dias contributed to this report.

Jenna DeAngelis