NEW YORK, Sept. 20 (UPI) -- He was born in Afghanistan, immigrated to the United States with his family in the mid-1990s and became a naturalized citizen five years ago -- but that was also the same time friends and family members say Ahmad Khan Rahami started to turn into someone they didn't recognize.
Now, the 28-year-old suspect is shackled to a hospital bed and facing numerous federal criminal charges for allegedly bombing three New York City-area targets over the weekend.
Federal agents and New York authorities delved into Rahami's background on Tuesday to determine whether he perpetrated the attacks by himself, or possibly had help along the way.
In federal court Tuesday afternoon, Rahami was charged with four counts, including use of weapons of mass destruction and bombing a place of public use.
The federal charges are in addition to several state counts that include attempted murder of a law enforcement officer.
In the meantime, investigators are speaking to family members and acquaintances to try and fill in Rahami's background -- and much of what they've learned so far appears to paint a picture of a young man's radical transformation.
At age 23, Rahami traveled to Afghanistan in 2011 -- the same year he received U.S. citizenship. Investigators say by this time, he began displaying a harder pro-jihad mentality.
When he returned, family members say Rahami barely resembled the man they'd come to know. His father said Tuesday his son was violent toward other family members "for no reason." In fact, the father said he called the FBI about it in 2014, The Washington Post reported. Rahami was also jailed on one occasion for domestic violence.
The exact sequence of events and how far Rahami's father went with the FBI, however, remains unclear. After telling reporters he'd contacted the bureau about his son, the father appeared to downplay the matter and said it was a misunderstanding, CNN reported Tuesday.
FBI records indicate Rahami was never interviewed by agents and he was never placed on a list of potential terrorists.
Investigators say Rahami acquired a keen interest in terror-related activities and past events, such as the 2013 Boston Marathon attack, the 2011 death of al-Qaida leader Anwar al-Awlaki and the 2009 Fort Hood shooting in Texas.
Those interests have gotten investigators wondering if anyone else might have contributed to the weekend's violence, which local and federal officials say was a terrorist act.
"Now that we have this suspect in custody, the investigation can focus on other aspects, such as whether this individual acted alone and what his motivations may have been," New York City Police Commissioner James P. O'Neill said Tuesday.
Rahami faces numerous criminal charges, including attempted murder of a law enforcement officer, stemming from the explosions on Saturday and Sunday, and his capture Monday. Twenty-nine people were injured in the Manhattan blast.
Police said he shot two responding police officers -- one in his Kevlar vest -- but neither was seriously injured. Rahami was himself shot in the shoulder during the gun fight.
Rahami arrived in the United States as a child in 1995 after his father came seeking asylum. Officials say he took extended trips to Afghanistan and Pakistan in 2011 -- and visited Kandahar and the Taliban stronghold of Quetta. He returned to Pakistan in 2013 and spent about a year there.
Rahami told immigration officials upon his return that he visited family during the trips. Authorities now believe that time overseas most likely was when he became radicalized to the point of advocating violence.
Investigators are trying to determine whether he had received any operational assistance or inspiration from his trips abroad. So far, they have found no evidence of cooperation with any established terror group.
Rahami married a Pakistani woman during his trip in 2011 and brought her, legally, into the United States a year later. Officials said she left and returned to Pakistan just days before Saturday's attacks. They are working with Pakistan officials to gain access to her.