This is a good example of how tricky it is to pin down just when a "code word", epithet; or indeed ANY quotation first came into use. Even with huge full text databases such as Google Books or commercial full text such as Ebsco databases, JSTOR, and Project Muse; or Factiva, Lexis Nexis Academic, Proquest, and other newspaper full text databases, we are generally depending on fairly unreliable Optical Character Recognition (OCR) searches. We very likely will miss many words that simply don't get picked up by the search software. If you are near a large academic library where you can try them out, you will notice striking differences in search results for EQUIVALENT searches of the same newspaper (same date range) in Factiva, Lexis, or Proquest, for example.
Factiva (a larger newspaper database than Lexis Academic, a journalism librarian colleague informs me) gets 38 hits in "all dates" for the search: "no human involved". The oldest one related to criminology is no. 37; "PROSECUTOR BLASTS MENENDEZES AS 'VICIOUS BRATS'. Linda Deutsch Associated Press. 669 words 12 December 1993 Los Angeles Daily News. This has a quote from Deputy District Attorney Pamela Bozanich: "While admitting that the Menendez family was "not an Ozzie and Harriet family where everyone was happy," she said the parents gave them the privileges of wealth. "The parents were willing to support them while they were spoiled, vicious brats," she said. She accused defense attorneys of using a tactic called NHI, a homicide detectives' sarcastic shorthand for worthless victims meaning "No human involved." "It is a sick kind of joke and that's what the defense is in this case. What the defense is saying is that Jose and Mary Louise Menendez were such horrible people, it's OK. Who cares if they are dead? The world is probably a better place without them."
Lexis Academic/ Legal/ Law Reviews, US and Canada gets 11 hits (all dates) for the search: "no human involved". The oldest is: Wisconsin Law Review, 1995, 1995 Wis. L. Rev. 1003. 19859 words. "ARTICLES: MULES, MADONNAS, BABIES, BATHWATER, RACIAL IMAGERY AND STEREOTYPES: THE AFRICAN-AMERICAN WOMAN AND THE BATTERED WOMAN SYNDROME." Linda L. Ammons. It has a quote in footnote 168:
"n168 See John C. Brigham, Racial Stereotypes, Measurement Variables and the Stereotype-Attitude Relationship, 2 J. Applied Soc. Psychol. 63 (1972). Los Angeles police are not the only law enforcement officers known for their racist epithets. In an interview with CBS news, Miami attorney H.T. Smith decoded "NHI," a reference to African-Americans by Miami police. NHI meant "no human involved." See Itabari Njeri, Words to Live or Die By: Mapping the Psychological Landscape of a Scarred Los Angeles, L.A. Times, May 31, 1992, at 23. Racist "cop talk" is a national problem. See Don't Tolerate Police Racism, S.F. Chron., Nov. 11, 1991, at 20A; Karen Fernan, Police Attempt to Curb Racist "Cop Talk," Phoenix Gazette, June 30, 1993, at B5; NAACP Charges Police Racism, Evidence Shows Growing Brutality Against Minorities, Report Says, St. Louis Post Dispatch, Apr. 1, 1993, at 10A."
Many of the other 10 Law Review articles have very good links to other sources of the term – not only as a racist "code word", but also in reference to any people not regarded as worthy of "personhood" – prostitute rape victims, extremely violent criminals in prisons, etc.; clearly some uses of the term may seem less forgivable or understandable than others.
Academic Search Premier (Ebsco, available at virtually all academic and some public libraries) gets 5 hits for the search: "no human involved" if you select a field TX-all text, in Advanced Search. Several mention Barbara Seranella's first novel, "No Human Involved," set in Los Angeles in the 1970s. See short review in Publishers Weekly; 06/16/97, Vol. 244 Issue 24, p49, 1/5p "Forecasts: Fiction". Brainard, Dulcy and
Steinberg, Sybil S.
Oxford English Dictionary (Advanced Search - full text) for "no human involved" gets us back to 1973 under the very long entry for N, which includes many acronyms beginning with N:
"NHI n. U.S. Police slang no humans involved, an informal classification assigned to a crime giving it low priority because its victim is regarded as having a low social status.
1973 J. WAMBAUGH Blue Knight ix. 124 Herb hated the drunk wagon. 'Niggers and white garbage,' he'd repeat over and over when something made him mad which was most of the time. And he called the wagon job 'the *N.H.I. detail'. When you asked him what that stood for he'd say 'No Humans Involved', and then he let out that donkey bray of his. 1989 Los Angeles Times (Nexis) 14 May, Police expend little sympathy on criminal-to-criminal mayhem. An acronym drifts unwritten about the system; those are NHI crimes No Human Involved. 1992 Ms. Sept. 69/4 Five San Diego artists say 'NHI' is police jargon for crimes against 'inhuman' people: prostitutes, informants, and drug users. 2000 Irish Times (Nexis) 4 Mar., 'NHI', said the LA guy, 'means "no humans involved."' The term, he said, is accepted police and CP industry jargon for when one drug dealer kills another."
Also try the 97 unique hits (of 149) in Google Books; especially the 56 (of65) limited preview and full view ones, for the search: "no human involved". If you try the plural, "no humans involved" gets 154 (of 275) including 76(of 139) "limited or full view"