MUSKOGEE, Okla. (AP) -- The man who confessed to the sniper shootings of two campers in 2003 is bipolar and hears voices, a psychologist said Tuesday in federal court in Muskogee.

Testimony continued in the sentencing trial of Edward Leon Fields Jr. He pleaded guilty last month to the first-degree murder of Charles and Shirley Chick.

Prosecutors are seeking the death penalty. Jurors also have the option of life in prison without possibility of release. Testimony will continue today.

A family doctor diagnosed Fields with depression three months before the slayings, said Dr. Bradley Grinage, a forensic psychiatrist hired by defense lawyers.

Fields wore a camouflage suit when he crawled on his belly to an Ouachita National Forest campsite and shot the Hurst, Texas, couple.

Fields told doctors he heard a man's voice say "just shoot them" over and over, until the killings were complete, Grinage testified.