Somalis in a central Minnesota city are trying to square the bright, family-minded young man who went to the mall to buy the new iPhone with the emotionless man who stabbed 10 people and in death is the subject of a terrorism investigation.

The aftermath of Saturday's attack at Crossroads Center Mall in St. Cloud also is testing longstanding efforts to improve strained relations between thousands of Somalis and other residents in the city. Several Somalis said they saw pickups driving through predominantly Somali neighborhoods the night after the attack, waving confederate flags and honking.

It's still unclear what led 20-year-old Dahir Adan to stab several people with what appeared to be a kitchen knife before he was confronted and killed by an off-duty police officer. Investigators are poring through witness and victim accounts, video footage and Adan's electronic devices to piece it together — determining whether an Islamic State-run news agency's claim that the attacker was a "soldier of the Islamic State" is true.

"We don't know the rest of the connection. Did he get angry with someone and lose his mind?" said Abdul Kulane, a local community leader and friend of the Adan family. "We are all shocked because we don't know what kind of strife could cause him to do this."

St. Cloud's police chief has said it seems Adan acted alone. On Tuesday, the FBI's Joint Terrorism Task Force assumed the lead on the investigation. FBI spokesman Kyle Loven said he could not discuss any investigative details, but that authorities are following up on all leads.

"Motivation is a big part of this investigation," Loven said.

As many as 10,000 Somalis have settled in three counties that compose St. Cloud, a city with about 65,000 people, according to estimates from the state demographer. Smaller Somali populations have settled in rural pockets of Minnesota, while Minneapolis has the state's largest Somali population; conflict between those residents and the state's majority population seem to occur less frequently than in Minnesota's smaller cities.

But south of the Twin Cities, the owner of a restaurant and ice cream parlor changed his sign out front after Saturday's attack to read "Muslims Get Out," saying he won't be "peer pressured by the politically correct crowd."

And aside from the reported Confederate flag situation, St. Cloud has had lasting issues. Last year, some Somali-American students walked out in protest, saying they were being harassed and called members of Islamic State. Complaints of mistreatment at a local high school prompted a federal civil rights investigation in 2011 and, though a 2011 agreement resolved that case, the U.S. Department of Education still was monitoring last year.

Adan, who was described by community members as an honor roll student in high school and a man who helped his family, reportedly asked victims if they were Muslim before stabbing them, and lunged at Avon police officer Jason Falconer before being shot. St. Cloud Mayor Dave Kleis called Adan "an individual clearly bent on evil" at a news conference on Tuesday.

But Kleis also insisted the city is united and said he hasn't heard of any retaliatory incidents since the stabbings.

Nor has Jaylani Hussein, the executive director of Council of American-Islamic Relations' Minnesota chapter, who said some local Somali-Americans were nervous about being viewed as "guilty by association."

"This is the test that we need to show that this community is stronger and more resilient than what has been reported," Hussein said.

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Associated Press writer Amy Forliti contributed to this report.