FULL NAME: UNKNOWN (MONIKER “3-X”)
KNOWN ALIASES: 3-X, 3X, THE 3-X KILLER, RED DIAMOND ASSASSIN, AGENT OF THE “RUSSIAN RED DIAMOND SOCIETY” (CLAIMED)
DOB: Unknown
DOD: Unknown
PRIMARY RESIDENCE: Unknown; activity centered in Queens and Brooklyn, New York, United States
PHYSICAL DESCRIPTION: Male, approximately 5’6”, thin face, noticeable teeth, strong foreign accent (possibly German or Eastern European), well-dressed and composed under stress according to witnesses
CRIMINAL TYPE: POWER/CONTROL KILLER WITH MISSION-ORIENTED ELEMENTS
ACTIVITY RANGE: June 11 – June 21, 1930 (verified); related communications through 1931; single confession in 1936 unproven
CURRENT STATUS: Unidentified, presumed deceased
BACKGROUND
In June 1930, the city of New York was shaken by a pair of strange, calculated murders that bore a cryptic signature: “3-X.” The press labeled the unknown gunman the 3-X Killer after typed notes and letters began arriving at newspapers and police stations, each bearing the same mark. The author claimed to represent a secret cabal called the “Russian Red Diamond Society,” whose supposed mission was to punish traitors and retrieve stolen “documents of international importance.” The story had all the drama of pulp fiction, yet two men lay dead in their parked cars, and two female companions swore they had looked the killer in the eye.
The killings followed a ritual pattern. Each victim was a man sitting with a woman on a quiet Queens street. The assailant approached calmly, verified the man’s identity, shot him at close range, then courteously escorted the woman to a nearby bus stop and handed her a stamped or typed note instructing her to read it later. Within hours, newspapers received letters typed on the same stationery, signed “3-X.” The killer’s correspondence described his actions as part of a larger “mission” for the Red Diamond Society and warned that more deaths would follow.
Police quickly concluded that the letters and the shootings were connected. Ballistics confirmed that both murders were committed with the same .32-caliber revolver. Detectives also determined that the alleged secret society existed only on paper. The letters, filled with melodramatic phrasing and self-importance, appeared to be the invention of one man seeking control, not an organization pursuing espionage.
INCIDENTS
1. THE MOZYNSKI MURDER – JUNE 11, 1930
Joseph Mozynski, a Queens grocer, was parked with companion Catherine May when a polite stranger approached the driver’s side window. Without warning he fired twice, killing Mozynski instantly. He then turned to May, assured her she would not be harmed, and handed her a sealed envelope. Inside was a sheet stamped in red ink: “Joseph Mozynski – 3-X – 3-X-097.” The killer ordered her to open it the next day, escorted her to a bus stop, and vanished into the darkness. That same morning the New York Evening Journal received a letter claiming responsibility, insisting the killing had been “the first act of justice” carried out by agents of the Red Diamond Society.
2. THE SOWLEY MURDER – JUNE 17, 1930
Six days later salesman Noel Sowley sat in his car with Elizabeth Ring on another secluded Queens street. The same man appeared, demanded Sowley’s driver’s license, examined it, and said evenly, “You are going to get what Joe got.” Two gunshots followed. Sowley died instantly. A newspaper clipping about the Mozynski case was discovered in his pocket, and Ring was given another note bearing the 3-X stamp. Ballistics tied the bullets to the same weapon used in the first attack. Panic swept the borough; citizens avoided parked-car rendezvous, and the city ordered a night patrol of lovers’ lanes.
3. THE THREATENED THIRD MURDER – JUNE 18–19, 1930
Letters reached both the police and the press predicting a “third Queens killing.” Commissioner Grover Whalen mobilized more than 300 patrolmen across Queens and Brooklyn, turning the borough into a trap for the self-styled assassin. That night a separate shooting occurred in Brooklyn involving insurance broker Morris Horwitz, who was wounded but survived. Newspapers speculated he was “the third mark,” but investigators found no direct connection beyond coincidence.
4. THE FINAL LETTERS – JUNE 21, 1930
Two more letters arrived claiming the “mission” was complete and announcing the killer’s planned return to Europe. The author boasted that the Red Diamond Society had recovered its stolen secrets and declared, “You will hear no more from 3-X.” True to his word, the letters and killings stopped.
5. AFTERMATH AND FALSE LEADS
For months detectives pursued tips ranging from disgruntled business rivals to ex-spies. They examined handwriting samples, questioned known eccentrics, and trailed numerous “foreign gentlemen” reported by frightened residents. None fit the composite description. In 1931, a brief letter surfaced signed “3-X,” threatening to resume killings; it contained authentic phrasing but led nowhere. In 1936, a Lake Placid lifeguard named Frank Engle confessed after heavy questioning, but inconsistencies and lack of physical evidence forced authorities to release him. The 3-X file was quietly closed soon after.
TIMELINE OF EVENTS
June 11 1930: Joseph Mozynski murdered, Catherine May spared. First 3-X letter received by Evening Journal. June 17 1930: Noel Sowley murdered, Elizabeth Ring spared. Ballistics confirm same weapon. June 18 1930: Threat of third murder; citywide patrols activated. June 19 1930: Horwitz shooting in Brooklyn, uncertain link. June 21 1930: Letters proclaim mission accomplished; killer claims to leave country. Oct 1931: Final unsigned note believed from same author; no further action. June 2 1936: Frank Engle confession deemed unreliable; case unsolved.
POSSIBLE SUSPECTS
FRANK ENGLE: His confession included minor accurate details, possibly gleaned from newspaper reports. Psychiatrists described him as unstable. He recanted under further questioning.
LOCAL OFFENDER THEORY: Many investigators believed the Red Diamond Society story was pure fabrication, used by a local gunman to conceal a personal motive—perhaps jealousy, business revenge, or thrill seeking. The killer’s calm behavior, his control over witnesses, and his flourish of symbolism all pointed to a manipulative, organized personality rather than a political operative.
CULTURAL IMPACT
The 3-X case bridged the era between early twentieth-century “mystery assassins” and the later publicity-driven serial offenders who manipulated media. Newspapers of 1930 devoted entire front pages to the stamped 3-X letters, treating them as serialized fiction. The case faded from memory after the Great Depression diverted attention, but historians later noted its striking resemblance to the media taunting tactics of the Zodiac Killer four decades later. The New York Evening Journal’s sensational coverage introduced public fascination with coded killers long before the term “serial killer” existed.
Today, the 3-X murders stand as one of New York’s earliest unsolved double homicides linked by both forensic and communicative evidence. The mystery endures precisely because the killer vanished without trace, leaving only a few typed sheets of paper, a mythic “secret society,” and two unsolved deaths.
KILLER THEORY
Behavioral analysts categorize 3-X as a power/control killer with mission-oriented pretensions. His victims fit no ideological profile beyond being accessible males accompanied by women, suggesting opportunity and symbolic punishment rather than espionage. The ritual of sparing the female companion and delivering a written token indicates a desire to dominate psychologically, to witness fear and obedience. The elaborate “Red Diamond Society” narrative functioned as camouflage and self-mythologizing, granting moral justification to acts of murder.
Unlike impulsive spree offenders, 3-X demonstrated planning: he selected isolated areas, verified identities, and neutralized witnesses without physical harm. His letters reveal narcissistic grandiosity and linguistic flourishes consistent with educated self-dramatization. The abrupt cessation implies either flight, institutionalization, or suicide. Investigators later speculated he may have achieved what he sought—public recognition without capture—and therefore ended his campaign.
The 3-X case remains a study in how one calculated individual exploited media to extend terror beyond his physical crimes. The killer’s precise identity has never been determined, but the pattern he established—communication, control, and constructed mythology—set the stage for future criminals who weaponized the press.
SOURCES
The True Crime Database: “3-X Murders – The Red Diamond Assassin.” Contemporary press archives: New York Evening Journal (June 1930), Brooklyn Daily Eagle, New York Times archives (June 1930 – June 1936). NYC Police Department historical summaries, Queens DA case archives (public domain). Federal Bureau of Investigation historical behavioral analysis reference, Media Interaction in Early Serial Crimes (1979).
