The FBI says the 20-year-old man who stabbed 10 people last month at Crossroads Mall may have become radicalized recently and that the attack likely was premeditated.

FBI Special Agent Rick Thornton said Thursday at a news conference that Dahir Ahmed Adan took interest recently in Islam, withdrew from his friends and encouraged female relatives to be more religious.

Thornton also said investigators were told that Adan yelled "Islam, Islam" during the attack.

Thornton said the investigation is ongoing, including his online history, and that authorities are trying to obtain permission to unlock Adan’s iPhone.

FBI Director James Comey said last week it appeared Adan was at least partly inspired by extremist ideology.