Lust

S4 E4: The body of a woman in her 60's is found mangled in Central Park. It's hard to make an identification and it isn't until they find her dog that they can figure out who she is - Greta Esterman, a doctor with the public health department. Greta's job was notifying victims who had contracted HIV and other sexually transmitted diseases that they were infected, and apparently she had quite a few enemies, and had even received threatening phone calls. Her grieving husband Arthur Esterman (Michael Gross) tells Detectives Stabler (Christopher Meloni) and Benson (Mariska Hargitay) that one caller, Roger Pomerantz (Brian Rogalski), was particularly vile. Roger was just released from prison, but he has an airtight alibi.