UPLAND, Calif. – Three of the young men swept up in a federal terrorism probe grew up in the Southern California suburbs where they played pick-up basketball, ran for homecoming court and sparred in video games with neighborhood kids – a far cry from the wannabe terrorists described by the FBI.

Two of the men converted to Islam less than two years ago and the third, an American-born Vietnamese Muslim, drifted into their orbit as recently as September after a game of paintball. He also is an unemployed high school dropout and new father.

The rapid evolution from suburban teen to aspiring jihadist alleged in court documents blindsided family members, but experts who study homegrown terrorism said the case highlights the susceptibility of new converts to radicalization, particularly among the young.