They were alike in many ways. Boston Marathon bomber Tamerlan Tsarnaev and Ahmad Khan Rahami were both in their late 20s, born abroad, and lived with families that struggled to acclimate. They both traveled to their home countries and came back to America with radical views of Islam. They both were looked at by the FBI.
And each of them, authorities said, went on to carry out similar terror attacks. They built pipe bombs, and remotely detonated pressure cookers laced with shrapnel. In Tsarnaev's case, he attacked the Boston Marathon in April 2013 with his younger brother. Rahami allegedly planted bombs in a New York neighborhood and a New Jersey seaside town, by a charity race to benefit Marines. His fingerprints and DNA were found at the Manhattan bombing, authorities have said, and, like Tsarnaev, he was identified in surveillance video, leading to a manhunt for his arrest.
Law enforcement and terrorism analysts said Tuesday that the frightening similarities could help serve as a blueprint for combating terrorism, or at least identifying suspects, as authorities struggle to develop a meaningful profile of a homegrown terrorist.
"It appears the motivations are the same," said Edward F. Davis, who was Boston's police commissioner at the time of the Marathon bombings.
He sees a checklist of sorts: a person has problems with authorities and the government; they may have traveled abroad recently; they developed radical ideologies, often accompanied with a change in lifestyle and clothing. In New Jersey, members of the Muslim community have painted such a profile of Rahami.
"We have to look at identifying and deprogramming people who go down this road," Davis said. "If we can do more outreach to these communities, and get them to identify people before something happens, I think that's a strategy we need to employ."
Former Massachusetts State Police colonel Timothy Alben, who held that post at the time of the Marathon bombings, said that the simplicity in which the similar attacks were carried out is cause for concern: The bombs that the Tsarnaev brothers and Rahim used were made with common household items.
"The fact of how easy it is to do this . . . we, in law enforcement and homeland security, have to think about this," he said. "It's all very familiar, it's almost a blueprint."
Authorities said Tuesday that Rahami has no apparent ties to the Marathon bombings, and contradicted media reports that he mentioned the Tsarnaev brothers in a notebook.
"At this point in time, the investigation in New York has revealed no connection or reference to the Boston Marathon bombers or bombings," said Kristen Setera, a spokeswoman for the FBI in Boston.
Rahami, 28, who lived with his family above a fried chicken restaurant they ran in New Jersey, is being held on $5.2 million bail.
Authorities said that they have no other suspects at large or evidence of a local terrorism cell, but cautioned that they are still investigating.
What has emerged is a profile of a homegrown terrorist, a lone wolf who embraced extremist views of Islam so radical it worried those around them. The Associated Press, citing an anonymous law enforcement official, reported Tuesday that the FBI looked into Rahami two years ago after his father called with concerns that his son was a terrorist. The father later retracted that claim, though, and told investigators he just meant his son was hanging out with the wrong crowd.
The disclosure of the father's contact with the FBI raises questions about whether there was anything more law enforcement could have done at the time to determine whether Rahami had terrorist aspirations, the Associated Press reported.
Similar questions were raised with the FBI's handling of Omar Mateen, after he killed 49 people at an Orlando nightclub in June. The FBI disclosed that it had earlier sent in undercover agents to investigate him, but that they did not find enough information to charge him.
Multiple media outlets also reported that Rahami made rambling references in a journal to Anwar al-Awlaki, the Yemeni-American propagandist for Al Qaeda, who died in a drone strike in Yemen in 2011. He was a source of inspiration for many radicals in the United States, including the San Bernardino, Calif., shooter Syed Rizwan Farook; Mateen, the Orlando shooter; and for Tsarnaev and his younger brother, Dzhokhar Tsarnaev.
Tamerlan Tsarnaev, 26, died days after the Marathon bombings, during a shootout with police in Watertown while trying to flee the area. His younger brother was sentenced to death last year, but is appealing the sentence. At trial, his lawyers argued that Tamerlan was the mastermind.
Authorities also disclosed after the Marathon bombings that the FBI had been alerted by Russian authorities that Tamerlan was developing radical views after a trip there, but the information was not enough to sustain an investigation.
Seamus Hughes, deputy director of the Program on Extremism at George Washington University's Center for Cyber & Homeland Security, said such cases point to the difficulty the FBI faces in determining true threats. In each of the recent cases, the FBI had only conducted assessments, the lowest level of scrutiny before a full investigation is opened.
Hughes said the FBI cannot levy charges against everyone who travels abroad and returns with radical views — "You're going to find a lot of people who fit that profile," he said — but he added that the common thread in recent attacks is that the perpetrators were at one point questioned by the FBI.
"It's entirely possible there's a systemic issue that needs to be addressed," he said.