A Minnesota man who posed as a police officer and knocked on lawmakers' doors in the middle of the night, killing the top Democrat in the state House and her husband and wounding a state senator and his wife, pleaded guilty to murder on Thursday so that federal prosecutors would not seek the death penalty.

U.S. prosecutors said Wednesday they will not seek the death penalty as part of a plea agreement with the man charged in the political assassinations of the top Democrat in the Minnesota House along with her husband, as well as the attempted murders of a state senator and his wife.