Bishop Paul Bradley of Kalamazoo, Mich., who served as an auxiliary bishop in Pittsburgh from 2004 to 2009, reacted to the shooting in a Twitter post.
"In the face of the awful tragedy in a Pittsburgh synagogue where at least eight people were murdered and dozens more traumatized, let us once more pray that God will take those killed into his merciful arms and grant them eternal rest. Let there be peace in the world and in our hearts," he said.
U.S. President Donald Trump also denounced the shootings.
"It's a terrible terrible thing what's going on with hate in our country, and frankly all over the world and something has be done," Trump told reporters. "It's just a shame to watch this and to see it for so many years, so much of it, it's a shame."
The president speculated that the presence of an armed guard could have changed the outcome.
"If they had an armed guard inside, they might have been able to stop him immediately," he said. "Isn't it a shame that we even have to think of that, inside of a temple or inside a church? But certainly the results might have been far better."
Pennsylvania Gov. Tom Wolf called the shooting "an absolute tragedy."
"These senseless acts of violence are not who we are as Americans," he said. "My thoughts right now are focused on the victims, their families and making sure law enforcement has every resource they need."
Denouncing the harm caused by "dangerous weapons," he called for action to "prevent these tragedies in the future."
"We cannot accept this violence as normal."
Pittsburgh Public Safety Director Wendell Hissrich said the shooting is being investigated as a possible hate crime and the FBI is leading the investigation.
In 2017 the Jewish Federation of Pittsburgh announced that it had hired former FBI agent Brad Orsini to provide security. He had spent a year conducting safety training at area Jewish day schools, synagogues and community groups, the Pittsburgh Gazette reports.
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This story was updated at 4:07 p.m. Eastern Time to include the USCCB statement from Cardinal DiNardo.