A gunman opened fire at a Pittsburgh synagogue on October 27, killing 11 people.
At least six other people were wounded, including four police officers, authorities said.
Police said a suspect was in custody after the attack at the Tree of Life Congregation in Pittsburgh's Squirrel Hill neighborhood.
A law enforcement official identified the suspect as Robert Bowers and said he is in his 40s.
U.S. President Donald Trump condemned what he described as an act of "hate" and praised the actions of law enforcement for doing "an outstanding job."
When asked by a reporter about gun control, Trump suggested that an armed guard inside the synagogue would have been able to stop the suspect.
Trump also said such shooters should receive the death penalty and "suffer the ultimate price."
Israeli Prime Minister Benjamin Netanyahu said he was "heartbroken and appalled" by the attack.
"The entire people of Israel grieve with the families of the dead," Netanyahu said. "We stand together with the Jewish community of Pittsburgh. We stand together with the American people in the face of this horrendous anti-Semitic brutality. And we all pray for the speedy recovery of the wounded."