Before Ahmad Khan Rahami planted bombs in New York and New Jersey, he bought bomb-making materials on eBay, linked to jihad-related videos from his public social-media account and was looked into by law enforcement agents, according to the Federal Bureau of Investigation. If only the authorities had connected the dots.

Bombings in New York and New Jersey over the weekend -- as well as the discovery of several unexploded devices -- have led authorities to believe there may be a terror cell at work in those two states, law enforcement officials told CNN Monday.

And a manhunt is under way for 28-year-old Ahmad Khan Rahami after New York police identified him as a suspect in connection with the bombing Saturday night in New York's Chelsea neighborhood, which wounded 29 people.

"On all accounts, the public safety first response to the shooting was exemplary. First responders acted with courage and discipline – using their training and skills to act quickly and decisively in a horrifying situation. The challenges that they faced were immense.

This report is intended to inform other departments and cities as they train, prepare, and respond to critical events. Key ‘Lessons Learned’ are summarized in this E-Report and further detailed in the technical report."

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The attack in Nice that killed more than 80 people is an example of a shift in tactics by terror groups who are encouraging followers in the West to stay home and wreak havoc with whatever means they have at their disposal.

The use of a truck to mow down victims in the French Riviera resort town late Thursday is part of a move to a do-it-yourself style terrorism used by lone wolfs or small terror cells to conduct attacks that require minimal planning and support, analysts say.