A gunman shot three people dead Sunday at a Jewish community centre and a retirement community in Kansas on the eve of Passover, police said.
The 70-year-old white male suspect, who is in custody, was not local and did not know the victims, Overland Park Police Department Chief John Douglass told reporters.
The bearded man used a shotgun in the assault and investigators, who are being assisted by the FBI, are trying to determine whether a handgun and assault rifle were involved.
Police officers took the suspect, who has not yet been formally identified, into custody at an elementary school in Overland Park outside Kansas City.
He was heard yelling "Heil Hitler" as officers escorted him away, local NBC television affiliate KSHB reported. Douglass refused to confirm the report.
FBI Special Agent in Charge Michael Kaste said investigators were looking into the incident as a "hate crime."
"We haven't ruled out anything," Kaste added.
"I don't want to say the terrorism word; this is three hours into it. It's only wise and prudent we use every resource we have."
Douglass refused to be drawn on whether the "unexpected" shooting was a hate crime, however.
"We know it's a vicious act of violence and you know, obviously, at two Jewish facilities one might make that assumption. We have to know more about it," the police chief said.
The first shooting at the Jewish Community Center of Greater Kansas City took place around 1:00 pm (1800 GMT) as youths auditioned for a play.
Rabbi Herbert Mandl, who serves as chaplain for the Overland Park Police Department, told CNN that the suspect asked people whether they were Jewish before opening fire.
He killed two people there -- one died on the spot and the other succumbed to injuries at a hospital.
The man then got in his car and headed to the Village Shalom assisted living center, where he killed a woman in her 70s about 15 minutes after the first shooting.
In addition to the three people killed, the suspect shot at two other people but missed them.
'Sad and tragic' day
"Today is a very sad and tragic day and certainly, there are no words to express the senselessness of what's happened this afternoon," Douglass said.
Shortly after the incident was initially reported, police dispatched vehicles to survey and secure all active Jewish sites in the city and other non-Jewish religious institutions.
At the Jewish community center, the shooting took place in a parking lot just outside a theater where local media said 75 people, most of them children, were inside.
They had been auditioning for "KC Superstar," a local singing competition based on "American Idol."
The Jewish center said it would be closed for the rest of the day Sunday and Monday. All programs were canceled as the center confirmed there had been a "shooting incident."
It was earlier placed on temporary lockdown but program participants have since been released.
"Our hearts go out to the families who have suffered loss on this tragic day," the center said on its website.
"Our heartfelt gratitude as well to all those in Kansas City and around the world who have expressed sympathy, concern and support."
The Jewish holiday of Passover begins Monday.