New York explosion: What we know — and don’t know

An explosion in the heart of New York's Chelsea neighborhood sent dozens to the hospital Saturday night. Shortly after the blast, a second explosive device was found a few blocks away, placing much of New York on edge.

Authorities have not yet taken anyone into custody for being involved with the blast. As a multi-agency investigation continues Sunday morning, local and federal authorities intend to keep looking for who's behind what New York Mayor Bill de Blasio characterized as an "intentional act" -- but one he believes isn't linked to a major terrorist organization.

Here's what we know about the explosion that rocked New York:

What happened in Chelsea?

What we know: Around 8:30 p.m. Saturday night, an explosion occurred at 23rd Street and 6th Avenue on Manhattan's west side. A law enforcement source, speaking with CNN on the condition of anonymity, said the blast came from an explosive device planted near a dumpster.

Surveillance footage of the explosion, including video from cameras at Orangetheory Fitness in Chelsea, captured bystanders running through the streets, ducking from debris as windows shattered all around.

As first responders arrived in Chelsea, reports surfaced for another explosive device on 23rd Street between 6th and 7th Avenues. However, the device did not detonate, and no one was injured.

What we don't know: Details about the origin of the explosive device are still uncertain. So is the motive behind the blast and the people responsible for its detonation.

How many people were hurt?

What we know: There were 29 victims injured during the explosion. Of those, 24 people went to several local hospitals, including Bellevue Hospital. Armed guards stopped incoming vehicles to the hospital, including ambulances, to make sure none posed a threat to the medical facility.

"Thankfully, none of these are life-threatening injuries and the 24 patients that have been removed are not in serious condition other than the one patient with a puncture wound," NYPD Commissioner James O'Neill said a press conference.

What we don't know: Some of the victims closest to the explosion were at a loss for how the blast occurred. This was the case for David Martinez, one of the 29 injured, who said he was "traumatized" after seeing his life flash before his eyes.

"I blacked out, and the next thing you know I'm in an ambulance," he said.

What's the latest on the investigation?

What we know: It was a busy first day for O'Neill, the police veteran who has just replaced Bill Bratton as New York's top cop. He ended day one in his new role without a suspect in custody for the explosion.

Regardless, de Blasio vowed that New York "will not be intimidated" in the face of a potential threat.

"We have in this city the most advanced anti-terror capacity of any city in this country and obviously the largest police force of any city in the country all ready to ensure our safety," De Blasio told reporters.

Police say they have obtained surveillance video from numerous local businesses near the explosion site. Investigators are now scouring those tapes in hopes of tracking down the person who planted the device, NYPD said.

As investigators watched for clues, local officers and federal agents shined flashlights and guided dogs through the streets in hopes of finding out further information about the explosion.

What we don't know: Much of NYPD's response last night involved bolstering its public-safety presence. More officers than usual covered the streets of New York, ensuring that people felt like they were safe, despite the earlier explosion. Now comes the hard part: finding out more about the potential suspect or suspects. NYPD so far has released sparse information about this part of its investigation. Expect more details today.

So, what actually caused the explosion?

What we know: The explosion was so loud that it reverberated across the Hudson River all the way to Hoboken, New Jersey, according to social media users.

"We smelled something, like an intense sulfur smell, and saw smoke coming out of this building," said Chelsea resident Danilo Gabrielli. "I saw pieces of metal -- not large, but not small either. A few friends of mine saw glass there."

Less than a mile away, NYPD officers received reports of a device that resembled a pressure cooker with dark-colored wiring, according to local and federal law enforcement officials.

According to NYPD, the department's bomb squad safely removed the explosive device at 27th Street early Sunday morning.

What we don't know: At the moment, NYPD has not provided many details about the device responsible for the first explosion.

Who's responsible for the explosion?

What we know: At his press conference late Saturday night, de Blasio ruled out the possibility of a terrorist group being associated with the explosion.

"There is no evidence at this point of a terror connection," de Blasio said.

What we don't know: So far, authorities have not made any information public about who might be behind the explosion. The NYPD upped its presences throughout the entire city as a precaution, even though de Blasio stressed there wasn't a "credible and specific threat" to New York last night.