Season 5, Episode 11, "Escape": A prisoner escapes and goes after the boy (the prisoner's son's half-brother) whose testimony put him in jail.
Role: The boy (now man) the prisoner is after.
2. Sarah Hyland
Season 3, Episode 1, "Repression": False memories lead to a woman accusing her father of molestation.
Role: The woman's younger sister.
Season 10, Episode 12, "Hothouse": Detectives think that Elsa, a young girl found killed, is connected to sex trafficking, but it's later revealed that she was a child prodigy who was murdered.
Role: Elsa's roommate and her murderer.
3. Julie Bowen
Season 10, Episode 1, "Trials": A foster child — who steals a van and is involved in a car chase — claims he's been abused, which leads to the case of a serial rapist.
Role: Guardian of the foster child and woman who unknowingly married her own rapist (yes, that's Luke Perry).
4. Ty Burrell
Season 3, Episode 15, "Execution": A serial killer is scheduled to be executed, but the detectives hope to use him to solve another murder case.
Role: Attorney.
5. Constance Wu
Season 8, Episode 7, "Underbelly": A series of similar tattoos on murder victims leads detectives to a pimp who is also a serial killer.
Role: A student who is mistaken for a prostitute.
6. Ian Somerhalder
Season 4, Episode 20, "Dominance": Several couples are found dead at a dinner party, and the detectives have to find the killer before he murders again.
Role: Murderer.
7. Rooney Mara
Season 7, Episode 20, "Fat": A teenage girl is assaulted by two siblings and the detectives investigate why it happened in the first place.
Role: Teenager who is assaulted (and it turns out she previously beat up and bullied the overweight brother of the two siblings).
8. Kate Mara
Season 2, Episode 9, "Pixies": A young gymnast is killed from blunt trauma to the head.
Role: Murderer/gymnast.
9. Chandra Wilson
Season 4, Episode 8, "Waste": The detectives investigate the rape (and resulting pregnancy) of a comatose patient.
Role: She's a nurse at the hospital.
Season 7, Episode 3, "911": Detectives race to find a young girl who calls 911 saying that she's locked in a room.
Role: FBI specialist who helps the detectives with the 911 phone signal.
10. Rainn Wilson
Season 4, Episode 8, "Waste": Also the episode where the detectives investigate the rape (and resulting pregnancy) of a comatose patient.
Role: He's a janitor.
11. Keke Palmer
Season 7, Episode 10, "Storm": A car accident leads the detectives to uncover a child molester who kidnapped young Hurricane Katrina victims.
Role: The victim and older sibling of her missing sister.
12. Emily Deschanel
Season 3, Episode 17, "Surveillance": A cellist is attacked in her apartment, and it's later revealed that a stalker has placed hidden cameras in her home.
Role: Victim/cellist.
13. Emily VanCamp
Season 8, Episode 14, "Dependent": A young woman (VanCamp) is a suspect in the murder of her mother, but she claims she can't remember anything.
Role: Daughter of the woman who was killed.
14. Jim Gaffigan
Season 2, Episode 15, "Countdown": The detectives are on the search for a young girl and her abductor.
Role: Suspect (who is guilty of many other things).
15. Zoe Saldana
Season 5, Episode 21, "Criminal": A criminology professor is accused in the murder of a local student.
Role: Daughter of the criminology professor.
16. Liza Weil
Season 3, Episode 5, "Tangled": Party guests find a murdered doctor and his wife, who was raped, and the detectives suspect his wife, his mistress, and/or the mistress's neighbor.
Role: The mistress who hires her neighbor to murder the doctor's wife (because the doctor told her to). Later, she kills her neighbor, who raped her.
17. Melissa Benoist
Season 12, Episode 5, "Wet": A PR executive at a soda company is poisoned.
Role: The woman who finds the body.
18. Laverne Cox
Season 9, Episode 16, "Closet": A gay man is murdered and the prime subject is a professional football player, who turns out to be his partner.
Role: Manager of a gym.
19. Hayden Panettiere
Season 2, Episode 11, "Abuse": The son of two famous singers dies and the detectives suspect parental neglect.
Role: Daughter of the couple.
Season 6, Episode 15, "Hooked": Lisa, a teenage girl who is involved in prostitution, is found murdered.
Role: Lisa's friend who is suspected of the murder (she didn't kill Lisa, but she killed someone else).
20. Elizabeth Banks
Season 3, Episode 7, "Sacrifice": A husband and wife who work in the porn industry as a way to pay for their daughter's medical bills are suspects in the case of a murdered porn producer.
Role: The wife and the murderer.
21. Norman Reedus
Season 7, Episode 22, "Influence": A bipolar teen accuses two classmates of rape and is later convinced by a rockstar to stop taking her medication.
Role: The rockstar.
22. Mae Whitman
Season 9, Episode 11, "Streetwise": After a debutante is murdered, the detectives investigate the "father" of a homeless "street family," who is suspected of murder.
Role: She's the mother (middle photo) of that street family and a former socialite (right photo) who is guilty of murder by proxy.
23. Pedro Pascal
Season 12, Episode 24, "Smoked": Days before a woman is set to take the stand against her accused rapist, she is shot and killed in front of her daughter.
Role: A dirty agent who supplies the murderer with the gun.
24. Kal Penn
Season 8, Episode 12, "Outsider": Fin works with a Brooklyn detective to catch a serial rapist who preys on women at Fin's son's college.
Status: Serial rapist and killer.
25. Kate Mulgrew
Season 7, Episode 21, "Web": An abused teenage boy — who runs a pornography ring — is kidnapped.
Role: A counselor from the U.S. Attorney's Office who wants to charge Teddy for making child porn.
26. Judy Reyes
Season 13, Episode 3, "Blood Brothers": A pregnant 13-year-old girl leads to an investigation of a politician, his son Tripp, and their family's secrets.
Role: The politician's housekeeper who had an affair with him, which resulted in a child who later goes on to murder the politician's other son, Tripp.
27. Will Arnett
Season 4, Episode 6, "Angels": A boy is found dead in the compartment of an airport bus, which leads the detectives to a child molestation ring.
Role: Human trafficker.
28. Abigail Breslin
Season 6, Episode 1, "Birthright": A woman kidnaps a child, who she believes to be her own daughter, which eventually leads to a custody battle.
Role: The young child.
29. Bradley Cooper
Season 6, Episode 20, "Night": An eccentric, wealthy man — whose protective mother is played by Angela Lansbury — is suspected of raping illegal immigrant women.
Role: The serial rapist's attorney.