The suspect in a spate of bombings that terrorised the New York City metropolitan area this weekend visited a city in Pakistan known for being a hotbed of insurgent activity, according ABC News.
The suspect, Ahmad Khan Rahami, was born in 1988 in Afghanistan and is a naturalised US citizen, according to the FBI.
Rahami spent time in Quetta, Pakistan, and Afghanistan during a trip that lasted nearly a year, from April 2013 to March 2014, the source said.
Quetta, a city of about two million people, is a known hot spot for insurgents and the reported home of the leadership of the Afghan Taliban.
"If they spent more than a few days, it raises suspicions that while they were there, they will have been recruited by terrorist groups," national security consultant Richard Clarke said on ABC News' "World News Tonight" Monday, referring to Rahami's travels to the area.
Afghan and US government officials say they believe Quetta has sheltered the Afghan Taliban's leadership since the US invasion forced them to flee the country in 2002. The Taliban's central leadership council, believed to be based there, is known as the Quetta Shura.
Officials say leaders there have planned and directed attacks across the border in Afghanistan and coordinated with terrorist groups like al Qaeda.
The area shares a major border crossing that leads to Kandahar in Afghanistan and is reported to be a transit point for extremists travelling in and out of Afghanistan and a hub for illegal trade crossing the porous and largely unsecured border.
Several al Qaeda militants have been killed or captured in the area, and the United States last year destroyed an al Qaeda base across the border in Kandahar province that it referred to as the largest militant training camp discovered in the history of the Afghanistan war.
Quetta also harbours a long-simmering insurgency against the Pakistani government. The city has seen a number of significant violent attacks and bombings, most recently last month when a blast killed more than 70 and injured over 100.