Mercy

S4 E14: Two men kayaking near Battery Park make the gruesome discovery, a cooler with a one-month-old dead baby inside. Based on materials found with the cooler, algae growth and current patterns, it is believed the baby was dropped uptown near Hudson University. After Detectives Benson (Mariska Hargitay) and Stabler (Christopher Meloni) cross-reference all pregnancies and account for all babies, they think they have their killer, Ellen Swanson (Heather Goldenhersh). She admits it was her 15-year-old sister Patty (Nathalie Paulding) who was pregnant, but the detectives discover Patty had an abortion. M.E. Warner (Tamara Tunie) then makes a shocking discovery - the baby had Tay-Sachs disease. A horribly gruesome genetic condition becoming fatal by the time a child reaches five years of age. The detectives now believe they are looking at a mercy killing.