Catholic leaders say the increase in executions in Missouri is a "grave concern."

The Catholic Bishops of Missouri called for steps to be taken to end the death penalty in a letter sent Wednesday to Gov. Jay Nixon, Attorney General Chris Koster, lawmaker and members of the state Supreme Court.

The letter noted that the state has executed 15 people since November 2013. The bishops said their "hearts go out to" the families of victims. But they questioned whether it was possible to thoroughly review each case when executions are carried out "so routinely."

The letter said pleas for clemency are "ignored," even when defendants have "severe mental illness or traumatic brain injury."

The bishops urged the recipients of the letter to "take a stand for life, mercy and justice"

Marina Nezhinkay