Crime scene investigators work at the scene of Saturday's explosion in Manhattan's Chelsea neighborhood, in New York, Sunday, Sept. 18, 2016. (AP Photo/Craig Ruttle)

Federal and local law enforcement agencies are investigating possible terrorist attacks in three states that occurred within about 12 hours on Saturday.

Around 9:35 a.m. ET, an explosive device was detonated in a garbage can in Seaside Park, New Jersey along the route of a Semper Five Marine charity run. No injuries were reported.

At 8:30 p.m. ET in the Chelsea neighborhood of Manhattan, a device that authorities say had components indicative of an improvised explosive device was set off in a dumpster, injuring 29 people.

A second device that appeared to be made from a pressure cooker was found a few blocks away. Investigators have not yet confirmed that it was related to the one that exploded.



Less than an hour after the explosion, around 9:15 p.m. ET, a man dressed in a private security uniform stabbed nine people in a St. Cloud, Minnesota shopping mall. He reportedly made references to Allah before being shot and killed by an off-duty police officer.

A St. Cloud police official said at a Sunday press conference that investigators are looking into whether there is a “nexus” to the other incidents, but no conclusions had been reached yet.

New York City Mayor Bill de Blasio told reporters Sunday that no possibilities have been ruled out, but it will take a lot more work to get to the truth.

“We’re not going to offer you easy answers,” he said. “We’re going to make sure we have all the facts.”

Although investigators are certain the detonation in Chelsea was an intentional act, de Blasio said they have not found evidence of a connection to international terrorism at this time.



As the FBI and the NYPD grapple with what one official called “a jigsaw puzzle of evidence” in Midtown, former FBI and counterterrorism officials say there are a number of things they will be looking for to identify who was responsible for the explosion and determine whether it is connected to the other incidents.

“There’s a tremendous amount of evidence you can get,” even from the bomb that did go off, said John Iannarelli, a former FBI official and author of “How to Spot a Terrorist Before It’s Too Late.”

Police may be able to reconstruct what was in the bomb and how it was made, looking at chemical residue, the wiring, and the trigger mechanism. There may still be fingerprints that can be lifted from the components.

If investigators can determine the signature--“the way the bomb is put together, including where it’s placed and how it’s placed”--Iannarelli said they can compare that information to past bombings and future attacks, as they did in the Unabomber case. They can also trace the components back to where they were purchased, which was a key step in identifying the Boston Marathon bombers.

This may prove challenging, but Iannarelli noted that investigators were able to prove that the 1988 Lockerbie bombing was caused by a bomb inside a transistor radio in a piece of luggage. That involved a crime scene strewn across several miles.



The placement of the bomb in a dumpster is a clue in itself, said retired FBI agent David Gomez, now a senior fellow at the George Washington University Center for Cyber and Homeland Security.

“It’s not an effective use of a bomb,” he said. “From a profiling standpoint, it shows an inexperienced bomb maker, no matter what happened.”

The dumpster helped contain the blast and the evidence, making the explosion less destructive and crime scene easier to process. The type of explosive, the wiring, and the trigger mechanism could all help identify the suspect.

The recovery of the second device nearby will be valuable if authorities conclude it is connected. Gomez said it will also be significant to establish whether that device was intentionally placed and hidden or simply abandoned for some reason.

Both devices will also be examined for possible links to the bomb used in New Jersey. CNN reported that some similarities have been found, but a connection is not confirmed.



“You look at every fiber of evidence around those two [explosions] for the connections,” Jeff Danik, a retired FBI counterterrorism official, said. That includes cell phone tower records that may establish if anyone was in the area of both explosions when they occurred.

“They better be pulling cell tower records like fiends,” he said.

A photograph of the unexploded device from Chelsea obtained by CNN shows a cell phone taped to the pressure cooker. That phone could also provide significant evidence.

“It’s fraught with problems for the bad guy because the phone has technology on it that if it’s not perfectly clean, there’s going to be a lot of leads,” Danik said.



The bomb maker probably has more devices and could be looking for more targets, so he said it would be helpful for authorities to release more photos, sketches, or other information about the devices used so the public knows what to look for.

John Cohen, a former counterterrorism coordinator for the Department of Homeland Security, said even if there is no direct link between the New York and New Jersey explosions, it still reflects the larger threat environment the nation now faces.

“Whether these events are operationally connected or not is really beside the point,” said Cohen, a professor at the Rutgers School of Criminal Justice.

“We need to think differently about the threat. There are common behavioral threads that we have seen,” he said.

The people who perpetrate this kind of attack are often seeking social connections and meaning in life, and their behavior leading up to acting is noticeable to their family and community if they know what to look for.



Cohen said law enforcement needs to look at terror suspects the same way the Secret Service deals with potential assassins and engage in “behavioral risk assessments” to stop them before they act.

“People don’t just go from flash to bang overnight. There’s usually a process they go through.”

This typically begins with adopting a cause or grievance, then increasing anger, then acquiring materials and preparing for the attack. At all of these stages, there is behavior that can be recognized. Cohen said it is important that the public know how to report their suspicions and that law enforcement have the training and capacity to respond effectively.

“You’ve seen an increased tempo in attacks committed by people who are inspired by extremist ideologies,” Cohen said, and their tactics are aimed at targeting as many people as possible.

The stabbings in St. Cloud are similar in that they are an attack on a soft target, but the tactics are different enough that experts say it could be a coincidence.

ISIS has claimed the attacker in Minnesota was “a soldier of the Islamic State,” but authorities are still working to confirm a motive. No claim of responsibility has been made for either of the explosions.



The attack in Minnesota occurred within 45 minutes after the Chelsea explosion. Not much was known about the explosion at that point, though, so Danik said the suspect may not have been aware of it yet when he set out to carry out his attack.

“It’s highly unlikely that you have such dissimilar types of events,” Gomez said. Coordination between the Chelsea bombing and the mall stabbing would also suggest a much greater capability to control events in the U.S. than ISIS has shown in the past.

If the mall attack had been a bomb, Iannarelli said a link would be more likely. He also cautioned against assuming that a claim of responsibility by ISIS means the group was actually involved.

“Anybody can claim responsibility,” he said, and ISIS wants people to “believe that they’re everywhere at all times.”

When a terrorist attack involves something as simple as a man with a knife walking into a mall or someone dropping an item in a trash can, experts agree it can be extremely difficult to prevent.

“It just shows how easy it can be,” Iannarelli said. “This is why we can’t just rely on law enforcement to solve all the problems, because they can’t be everywhere.”



That is an inherent risk of living in a free society, and it means the public needs to be vigilant.

“It’s not to be paranoid, but it’s just having a certain state of awareness and also knowing what to look for,” he said.

Following the Chelsea bombing, people may be more likely to report someone placing a suspicious package in a garbage can.

“The reality is you can’t prevent everything from happening, so you have to be prepared for worst case scenarios,” Iannarelli said.

Increased use of bomb-proof garbage cans might be an option to reduce the risk of this particular kind of attack.



When dealing with a slasher in a public place, though, experts offered the same advice often given for active shooter scenarios: run, hide, or fight.

“A guy with a knife in a mall, people have to run. That’s the best thing,” Danik said.

“If you can’t run, you can’t hide, you have to be prepared to fight back to the best of your ability,” Iannarelli said.