(CNN) -- A man with a history of spouting anti-Semitic rhetoric is suspected of shooting to death a boy and his grandfather outside a Jewish community center near Kansas City, Kansas, and then a woman at a nearby Jewish assisted living facility.
Police say Frazier Glenn Cross is the suspect in the shootings.
And investigators had "unquestionably determined" that his actions were a hate crime, said Overland Park Police Chief John Douglass.
Cross is the founder and former leader of the Carolina Knights of the Ku Klux Klan and the White Patriot Party, according to the Southern Poverty Law Center, which monitors hate groups. Both organizations operated as paramilitary groups in the 1980s, according to the SPLC.
In the 73-year-old's anti-Semitic and white-supremacist activities, he has also used the name Frazier Glenn Miller, the SPLC said.
After he was apprehended at a nearby elementary school, Cross sat in the back of a patrol car and shouted "Heil Hitler!" video from CNN affiliate KMBC shows.
For now, Cross faces charges of premeditated first-degree murder, officials said.
He obtained firearms from a "straw buyer," a middleman with a clean record who could buy weapons legally and then sell or give them to Cross, allowing Cross to avoid federal background checks, a U.S. law enforcement official said. He had three guns when he was arrested Sunday, authorities said.
Barry Grissom, the U.S. attorney for Kansas, told reporters Monday that he has "received communications" from U.S. Attorney General Eric Holder expressing Holder's "concern and condolences."
"We are in a very good place from an evidence standpoint of moving forward with this case and we will be presenting it to the grand jury in the not-too-distant future," Grissom said.
If the suspected shooter is charged and convicted of a hate crime, under federal law, the death penalty could be on the table. That would apply if the charge is that the defendant was motivated by the victims' "race, color, religion or national origin."
The shootings took place at the Jewish Community Center of Greater Kansas City and the Village Shalom Retirement Community in Overland Park a day before the start of Passover, a major Jewish holiday.
"The timing is terrible. The timing is awful," said Rabbi Herbert Mandl, a chaplain with the Overland Park police.
The police chief said the gunman shot at five people; none of whom he is believed to have known.
There were no other injuries, authorities said.
Police were investigating statements the man made after his arrest but declined to provide additional details, Douglass said.
The Anti-Defamation League said it warned last week of the increased possibility of violent attacks against community centers in the coming weeks, "which coincide both with the Passover holiday and Hitler's birthday on April 20, a day around which in the United States has historically been marked by extremist acts of violence and terrorism."
On Monday, the ADL reissued a security bulletin to synagogues and Jewish communal institutions across the country, urging them to review their security plans for the Passover holiday, which begins at sundown Monday.
'That idiot...knocked a family to its knees'
The shooting began just after 1 p.m. Sunday in the Jewish community center's parking lot.
Inside, the center was a hive of activity. A performance of "To Kill a Mockingbird" was about to begin, and auditions were under way for "KC Superstar," an "American Idol"-style contest for the best high school singer in the Kansas City area.
Outside, the gunman opened fire. Police said he was armed with a shotgun and may have been carrying other weapons. Reat Griffin Underwood, 14, was there to audition for the singing competition. His grandfather, William Lewis Corporon, was driving him. The bullets struck them in their car. Both died.
Reat was a high school freshman active in debate and theater. He loved singing and performing in his church's choir, his uncle said.
Corporon was a doctor who practiced family medicine in Oklahoma for many years before moving to the Kansas City area to be closer to his grandchildren, his family said.
"That idiot absolutely knocked a family to its knees for no reason," Reat's uncle and William's son, Will Corporon, said at a news conference Monday afternoon.
"My dad should be seeing patients today at his work. ... There is no reason. No reason for this. And it's just a tragedy."
Dr. Corporon worked 40 hours a week, and every free moment he had, he spent with his grandchildren, Will Corporon said.
"My father leaves a huge legacy of community and of healing," he said. "And it's just unbelievable that a senseless, stupid act can cause so much hurt and grief and pain."
Mother: 'They were ambushed'
Grandfather and grandson were Methodists, their pastor, the Rev. Adam Hamilton, told CNN on Monday.
Since the shooting, he has tried to comfort Mindy Losen, who is William Lewis Corporon's daughter and Reat's mother.
"They are devastated but they have a real deep faith and strength of conviction," Hamilton said. "They are overwhelmed with grief. They don't believe that this was God's will. This person was doing something evil and not keeping with God's will. They do believe that their loved ones are safe in the arms of God."
On Monday, Losen told reporters that she had been comforted by family, friends and faith.
"I feel confident from what I heard that they didn't feel anything. They didn't know what was coming. They were ambushed. ... It was a horrible act of violence," she said. "My dad, our dad, and my son were at the wrong place at the wrong time for a split second. And we want something good to come out of this."
As she mourns her son's death, she said she's hoping his organs can be used in transplants.
A woman caring for her mother
After the shooting started, the center went into lockdown.
"Some of these kids were taken into locker rooms and told to lay on the floor as the shots rang out," CNN affiliate KSHB reporter Lisa Benson told CNN.
Jeff Nessel, a parent, told The Kansas City Star he had just dropped his 10-year-old son off at the community center when a staff member told him to get back inside because there had been a shooting.
"We'll keep you on lockdown. You're safe here," Nessel said a staff member told him.
The gunman then drove to the retirement home, where he shot the third victim in the parking lot. Authorities identified her as Terri LaManno, who was visiting her mother as she usually did every Sunday at Village Shalom.
LaManno's Catholic church, St. Peter's Parish, posted a message on its web site calling LaManno "a loving mother and wife, and a gentle and giving woman."
The Children's Center for the Visually Impaired in Kansas City, where LaManno worked as an occupational therapist, described her as a "gracious, generous, skilled and deeply caring individual who made a great difference in the lives of so many children and their families."
'A raging anti-Semite'
Cross is a "raging anti-Semite" who has posted extensively in online forums that advocate exterminating Jews, the Southern Poverty Law Center said.
He has called Jews "swarthy, hairy, bow-legged, beady-eyed, parasitic midgets."
According to the SPLC, Cross founded and ran the Carolina Knights of the Ku Klux Klan in the 1980s. He was forced to shut down after the SPLC sued him for operating an illegal paramilitary organization and intimidating African-Americans.
He then formed another group, the White Patriot Party.
In the late 1980s, Cross spent three years in prison on weapons charges and for plotting the assassination of SPLC founder Morris Dees. The short sentence was a result of a plea bargain he struck with federal prosecutors. In exchange, he testified against 14 white supremacists in a sedition trial in Arkansas in 1988.
"He was reviled in white supremacist circles as a 'race traitor,' and, for a while, kept a low profile," according to an SPLC profile of him. "Now he's making a comeback with The Aryan Alternative, a racist tabloid he's been printing since 2005."
Connection with other shootings?
The Jewish center shootings come as a spate of highway shootings in the Kansas City area have many residents on edge.
Douglass said authorities don't have any information tying the highway shootings to Sunday's violence, but he said that's a possibility they'll consider.
"It's too early to tell," he told reporters on Sunday. "We have no active information that would lead us in that direction. But the investigation is so early, as you might imagine, we will be working with the Kansas City, Missouri, police department to cover any lead and if that's a possibility."
CNN's Matthew Stucker, Nick Valencia, Janet DiGiacomo, Evan Perez, Shimon Prokupecz and Don Lemon contributed to this report.