After a drug addict (Dee Freeman) brings in an audio tape she found on which a fatal shooting is heard, Lilly reopens a 1973 murder case involving the death of a 21-year-old rookie cop (Cory Hardrict). The young officer was shot three times in the chest while responding to a call at a drug-infested housing project. Also on the tape are the victim's final words: "Runner! Runner! Runner!"

When a young woman, Rosie (Laura Regan), wakes up from a coma, Lilly re-opens the fall in which her 6-year-old daughter Toya (Aynsley Lemon) died. Things get complicated when the mother remembers very little of that night, and Lilly feels especially motivated to find the killer, as Rosie was poor and living on welfare, reminding Lilly of her own past, and giving her an emotional bond to Rosie.

Rush and Valens re-open the case of a 25-year-old black woman, who was murdered in 1939, after the woman's granddaughter comes forward with new information. The woman was assumed to be a prostitute murdered by a client, but letters written by the victim indicate that she was afraid of a milkman.

The 1999 drowning death of a military academy's swim coach, which was originally ruled as accidental, is reinvestigated after the homicide division receives a note that suggests it was murder. Back at the office, Valens searches for Elisa after she goes missing.

Lilly and Valens reopen a presumed homicide from 1979 in which an unidentified victim's blood-drenched shoes, underwear and sheets were found in a trash bag, but no body. The investigation begins when a battered wife accuses her husband of murdering a girl in 1979 and brings in an amateur film from the time that supposedly shows him committing the crime.

The headless torso of a woman who disappeared in 1985, on the same day she filed domestic-abuse charges against her husband, is found by hikers in a wildlife preserve. The investigation quickly leads to the grisly discovery of 8 more decapitated bodies, the victims of a serial killer.

The unsolved 1963 murder of a black teenager, whose body was discovered by the then-young Will Jeffries, is reopened.

The discovery of nine human skulls leads Rush (Kathryn Morris) back to George Marks, the serial killer she was unable to incriminate months earlier, and who walked away a free man. As the detectives reinvestigate his mother's murder from 1972, George is forced to emerge from hiding to face Rush again. This time, their very lives are at stake in their final showdown.

Lilly re-opens the case of young girl, an overweight college freshman named Laurie, who died in a fraternity house fire in 2004. The fire was deemed accidental at the time, but a cell phone photo e-mailed from the girl's phone just moments before her death prompts a closer examination.

When a fisherman finds evidence of a young girl's death washed up on a shore in New Jersey, Lilly re-opens the 1965 case of 4-year-old child who had a seemingly abusive mother.

Lilly and the cold case team will have to decode the clues given by a twisted killer in order to save the life of a young boy who has been left to die alone. But first they must find the boy and for that they need to dig a little deeper into their own pasts.

Lilly investigates a 1995 shooting spree at a mall in which two teen boys killed 15 people before committing suicide. The case is reopened when a video of the crimes is found and it suggests that a third shooter was involved. Elsewhere, Stillman asks Valens to investigate whether Valens' brother may have been molested by a boxing coach in the 1980s.

In 2002, two kids were shot in front of two different schools on the same day at precisely 8:03 a.m. It's the fifth anniversary of the shootings, and Kat Miller wants to re-open the murders because she feels the cases are connected.

In the fourth season finale, a hostage situation arises when the entire team is held captive while they're investigating the 2006 killings of a family who had just moved into a new house.

Recovered from the shooting, Lilly wants to convince her boss that she's ready to get back to work. The team re-opens the 1994 case of three 10-year-old kids who were beaten to death when Lilly suspects the teens convicted of the killings may have been wrongfully incarcerated.

The team re-opens the 1982 case of a well-liked young man who was shot to death after being accused of date rape by several female college students.