According to criminal complaints filed in federal court, Ahmad Khan Rahami, the 28-year-old suspect in last weekend's attacks in New York and New Jersey, took inspiration from Osama Bin Laden and other terrorists and alluded to plans for revenge in a journal he kept.

That, according to some psychologists, follows a pattern of other attackers.

"There used to be the notion among the public that somehow these acts were spontaneous, just a reaction or highly emotionally-charged and very impulsive," said forensic psychologist J. Reid Meloy, a consultant with the FBI's behavior analysis unit and a professor at the University of California, San Diego.

"It turns out that they're not. These [plots] typically unfold over a period of time. There's lots of planning and preparation," said Meloy.

Along with a team of psychologists, Meloy has developed a guide of 8 warning signs of would-be terrorists, called "proximal warning behaviors" due to the close proximity in time in which they can usually be observed. They include: pathway, fixation, identification, novel aggression, and four other signs.

"The warning behaviors are there for law enforcement agencies to be able to look at and study and perhaps incorporate into their work," said Meloy.