Federal prosecutors have said that Robert Bowers who was arrested in connection with the Pittsburgh synagogue shooting on Saturday may face death penalty.
No fewer than 11 people were killed in the shooting while about six persons were injured.
Those injured included four police officers.
Already, Bowers, 46, has been charged with murder as he was accused of opening fire at the Tree of Life synagogue during its Sabbath service.
29 criminal counts charges have been filed against him.
The charges include the use of a firearm to commit murder.
Bowers was arrested by the police and treated in the hospital on Saturday after the shooting.
The synagogue serves the Squirrel Hill neighbourhood, which has one of the largest Jewish populations in Pennsylvania.
Pittsburgh’s Public Safety Director, Wendell Hissrich, described the scene of the shooting as horrific.
Bowers was said to be shouting anti-Semitic abuse as he entered the building, armed with an assault rifle and two pistols.
Reports said he barricaded himself in a room at the synagogue.
US President Donald Trump describe the shooting as very terrible, adding: “To see this happen again and again, for so many years, it’s just a shame.”
He said the US should “stiffen up our laws of the death penalty.”
“These people should pay the ultimate price. This has to stop,” he said.
He added that incident had little to do with US gun laws.
“If they had protection inside, maybe it could have been a different situation,” he said.
