PITTSBURGH — Lawyers for the suspect in the synagogue shooting that killed 11 people in Pittsburgh have challenged his potential death sentence as unconstitutional.

Lawyers for Robert Bowers argued in court papers filed last week that capital punishment violates the Fifth Amendment’s due process clause and the Eighth Amendment’s ban on cruel and unusual punishment.

They also said the practice of carrying out federal executions in state prisons violates a Tenth Amendment protection that says states can’t be made to enforce federal laws, a Pittsburgh newspaper reported Friday.

In court filings, Clarke said she has tried to negotiate a life sentence for Bowers but that prosecutors have rebuffed her.

Bowers is charged with killing 11 congregants during a Shabbat service at the Tree of Life synagogue on Oct. 27, 2018, and injuring six others, including four police officers.

He has pleaded not guilty to 63 federal counts, 22 of which carry the death penalty.

No trial date has been set.