Does a genealogy match prove who the killer is?

No. Under the Justice Department's interim policy, a genetic association from a genealogy service is used only as an investigative lead, and a suspect “shall not be arrested based solely on a genetic association.” The suspect's STR profile must be compared directly with the crime-scene profile uploaded to CODIS.

Why did the Green River sample take 14 years?

Detectives preserved the 1987 sample while they waited for DNA technology to improve enough to test it. The state crime lab began using a new DNA method on the Green River evidence in 2001.

Can an ordinary record end a murder case?

Yes. In 1998 a forged will left Kathleen Grundy's entire estate to her doctor, Harold Shipman, and her daughter took her suspicions to the police. The Shipman Inquiry concluded that the forging of her will “led directly to Shipman’s downfall.”

Why does the speed of a missing-person report matter?

Because the case starts with the report. Robert Piest's disappearance was reported to Des Plaines police the day he vanished, the court record shows, and a warrant to search John Wayne Gacy's house was issued two days later.

The Catch2 cases4 mechanisms

Killers are caught when their errors meet a system that can read them

The single mechanism that ends a case: a ticket, a sample, a sheath, a forged will.

The short answer

How do killers get caught?

In each catch in this series, a killer’s error met a system able to read it. A CODIS search releases a name only on a confirmed match with a known offender. Genealogy turns relatives’ DNA into an investigative lead. A record or a report counts once someone checks it or acts on it.^3,10

Timeline · The Catch

Errors, read in time

The line
Event

Notation

The line: Time, left to right. Down the screen on a phone.
Event: A fact on the record.
Missed chance: The system had him and let him go.
The catch: The error that ended it, knocked out of line.
Open case: No one charged.
A wait: Time passes and nothing moves.

Data table

Errors, read in time
Year	Event	Notation
1978	missing boy reported	Event
1998	forged will checked	Event
2001	stored sample tested	Event
2005	disk traced to church	Event
2018	genealogy names suspect	Event
2022	genealogy tip	Event

Mechanisms

4 in this series

The argument

The Catch

What do the catches in this series have in common?

Each pairs an error with a reader. In the Green River case, a saliva sample taken in 1987 waited 14 years for a DNA test able to read it. Robert Piest’s disappearance was reported the day he vanished, the court record shows, and a warrant to search John Wayne Gacy’s house followed two days later.^1,2,10

The error is the killer’s: a sample given, a record made, a victim who was missed at once. The reader is the system’s: a laboratory, a database, a search of records, an officer who acts on a report. When no one is reading, the error waits. The FBI says many deaths of the women Samuel Little confessed to killing were first ruled overdoses or attributed to accidental or undetermined causes.¹³

How do DNA databases close old cases?

A CODIS search produces a lead and a name only when it finds a confirmed match between a crime-scene profile and a known offender, the Justice Department says.³ The FBI says CODIS began as a pilot in 1990 and links serial violent crimes to each other and to known offenders.¹² A stored sample can also wait for a better test. In the Green River case, the state crime lab began using a new DNA method in 2001, and the arrest came that November.^1,2

How is genetic genealogy different from a database search?

Genetic genealogy looks for an unknown offender’s relatives among people who voluntarily put their DNA into genealogy services, then uses traditional genealogy research to generate a lead. Under Justice Department policy it may be tried only after CODIS searches fail to produce a probative and confirmed match, and a suspect “shall not be arrested based solely on a genetic association.”³

Janelle Cruz was killed in Irvine, California, in 1986.^4,14 In April 2018, authorities announced that genetic genealogy had identified Joseph DeAngelo, and he was arrested that month.^4,14,20 He pleaded guilty in 2020 to 13 counts of first-degree murder.^4,20

Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin were killed in Moscow, Idaho, on November 13, 2022.^5,21 A court order says the FBI’s genealogy work led to a tip to investigate Bryan Kohberger, and prosecutors said it pointed toward him but gave no substantive evidence of guilt.⁵ He pleaded guilty to four counts of first-degree murder in July 2025.^21,22

How can an ordinary record end a case?

After Stacy Moskowitz was shot in Brooklyn in 1977, a witness’s reminder about parking tickets on her street led police to David Berkowitz’s car, and he later pleaded guilty.^6,7 Kathleen Grundy, 81, died in June 1998, and a forged will left her entire estate to her doctor, Harold Shipman.^8,17 Her daughter took her suspicions to the police, and he was convicted in 2000 of 15 murders and of forging the will.^8,17

Ten people were killed in the Wichita area, the last of them Dolores Davis in 1991.^9,18 In 2005, a floppy disk sent to a television station was traced to a computer at Dennis Rader’s church, and he pleaded guilty to the 10 murders.^9,18,19

How fast can a report end a case?

Robert Piest, 15, vanished from a Des Plaines pharmacy on December 11, 1978.^10,15 Court records show police had the missing-person report that day and a warrant to search John Wayne Gacy’s house two days later.¹⁰ Gacy was arrested on December 21, ten days after Piest vanished, and was convicted of 33 murders.^10,11,15,16

The rule

A killer’s error is only half a catch. The other half is a system that reads it.

The cases

Filed under The Catch

The CatchNo. 02

The parking ticket only picked the date.

New York · 1976–1977

The CatchNo. 05

A criminology PhD student left his DNA at the scene.

Moscow, Idaho · 2022–2025

Questions

Does a genealogy match prove who the killer is?: No. Under the Justice Department’s interim policy, a genetic association from a genealogy service is used only as an investigative lead, and a suspect “shall not be arrested based solely on a genetic association.” The suspect’s STR profile must be compared directly with the crime-scene profile uploaded to CODIS.³
Why did the Green River sample take 14 years?: Detectives preserved the 1987 sample while they waited for DNA technology to improve enough to test it. The state crime lab began using a new DNA method on the Green River evidence in 2001.^1,2
Can an ordinary record end a murder case?: Yes. In 1998 a forged will left Kathleen Grundy’s entire estate to her doctor, Harold Shipman, and her daughter took her suspicions to the police. The Shipman Inquiry concluded that the forging of her will “led directly to Shipman’s downfall.”^8,17
Why does the speed of a missing-person report matter?: Because the case starts with the report. Robert Piest’s disappearance was reported to Des Plaines police the day he vanished, the court record shows, and a warrant to search John Wayne Gacy’s house was issued two days later.¹⁰

The record