Police said a suspect was in custody after a shooting caused "multiple casualties" at a Pittsburgh synagogue on October 27.
Three officers were also shot in the attack at the Tree of Life Congregation in Pittsburgh's Squirrel Hill neighborhood.
Local television station KDKA reported that at least eight people had died, "possibly more."
Police later identified the suspected shooter as Robert Bowers.
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 condemned the shooting.
"The entire people of Israel grieve with the families of the dead. 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," Netanyahu said.