Rex Heuermann, a Long Island architect, pleaded guilty to murdering seven women and admitted to an eighth victim. Heuermann will be sentenced to life in prison without parole.

A Long Island architect who led a secret life as a serial killer pleaded guilty on Wednesday to murdering seven women and admitted he killed an eighth in a string of long-unsolved crimes known as the Gilgo Beach killings. Rex Heuermann, 62, entered the pleas in a courtroom packed with reporters, police and victims’ relatives, some of whom wept as he detailed his crimes for the court. He will be sentenced to life in prison without the possibility of parole at a later date. Heuermann’s guilty...