“Gotcha” (“Got you!”) has been used since at least the early 1900s. William Safire’s “On Language” column in the New York (NY) Times has had its “Gotcha! Gang” (error spotters) by 1984.
   
On May 4, 1982, The Sun (London) used a “GOTCHA” front page headline for Great Britain sinking an Argentinean ship in the Falklands War. This is often referred to as the start of “gotcha journalism,” although the “gotcha” wasn’t a personal slip-up.
 
“Gotcha journalism” is cited in print from 1985 and was used often in the U.S. presidential campaign of 1992.
     
 
Wikipedia: Gotcha 
Gotcha is a relaxed pronunciation of “I got you” or “I’ve got you” usually referring to an unexpected capture or discovery.
 
Gotcha may also refer to:
(...)
. Gotcha (headline), a controversial frontpage headline which appeared in The Sun newspaper, on 4 May 1982
   
Wikipedia: Gotcha journalism
Gotcha journalism is a term used to describe methods of interviewing which are designed to entrap the interviewee into making statements which are damaging or discreditable to their cause, character, integrity, or reputation. The aim is to make film or sound recordings of the interview which can be selectively edited, compiled, and broadcast or published to show the subject in an unfavourable light.
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History
The phrase gotcha journalism is reported to have been come from a headline in the British tabloid newspaper The Sun in 1982, when it printed a massive headline reading “GOTCHA” in reference to an incident in the Falklands War (this headline was, in fact, gloating over a successful British attack and was not what later came to be called “gotcha journalism”).
 
An early citation indicated that “gotcha journalism” was used by Stuart K. Spencer in the Los Angeles Times in 1987.
 
Merriam-Webster Online Dictionary
Main Entry: got·cha
Pronunciation: \ˈgä-chə\
Function: noun
Etymology: alteration of got you
Date: 1974
: an unexpected usually disconcerting challenge, revelation, or catch; also : an attempt to embarrass, expose, or disgrace someone (as a politician) with a gotcha
   
(Oxford English Dictionary)
gotcha, gotcher
a representation of the colloq. or vulgar pronunciation of (I have) got you (see esp. GET v. 21a).
1932 E. WALLACE When Gangs came to London xxii. 197 The ‘plane was nearing the centre of Cavendish Square, when it suddenly heeled over. Its tail went down and it fell with a crash in the centre of the garden which occupied the middle of the square. ‘Gotcher!’ It was Jiggs’ triumphant voice.
1966 H. WAUGH Pure Poison (1967) xviii. 112 ‘Give her background a once-over on your way to Springfield… You might try for a record of her blood type first. She claims it’s O but she doesn’t carry any card.’ Wilks sighed. ‘I gotcha.’
   
14 September 1903, Daily News, (Marshall, MI), “The Vernacular,” pg. 2, col. 5:
“Yeh.” Gotcher money?”
“Yeh.”
“So vy. Gotcher aptite?”
“Yeh. Gotchours?”
(From the Chicago Tribune—ed.)
 
8 January 1908, New York (NY) Journal, pg. 4:
“I’ve gotcher booked.”
   
30 September 1911, Syracuse (NY) Herald, pg. 16, col. 5:
WIllie replied: “I gotcha, Steve, I gotcha!”
 
2 December 1911, San Antonio (TX) Light, pg. 4:
YES I GOT CHA.
(“Silk Hat Harry’s Divorce Suit” cartoon by TAD—ed.)
 
1 January 1912, Wilkes Barre (PA) Times Leader, pg. 11:
“I gotcha, Julius, but why LEAP year?”
 
13 June 1912, Grand Forks (ND) Herald, pg. 8:
“I gotcher, Steve!” he exclaimed in the latest American;...
 
25 November 1984, New York (NY) Times, “On Language” by William Safire, pg. SM13:
The copyreader was particularly fearful of the “Gotcha!” gang, the shock troops of the Nitpickers’ League, who take special glee in exposing errors in this space.
 
12 December 1984, New York (NY) Times, “On Language” by William Safire, pg. SM7:
The Gotcha! Gang Strikes
THE GOTCHA! GANG is that shock troop of Lexicographic Irregulars who specialize in correcting other language mavens. Their delight is catching grammarians with their syntax down; their symbol is the hoist petard, and their patron saint goes by the name of U. Ofallpeople.
   
Google Books
6 January 1985, Deseret News (Salt Lake City, UT), pg. E5, col. 2:
He (Ben Wattenberg—ed.) cites four main reasons for a Bad News Bias: commercial pressure, the adversarial nature of the press that leads to “gotcha journalism,” a post-Watergate mentality and a liberal tilt in the media.
 
2 October 1992, Indiana (PA) Gazette, “Perot back in the race for president,” pg. 4, col. 1:
The target of some blistering accounts about his business dealings earlier this year, Perot chastised reporters at one point for practicing “gotcha” journalism.
   
Google Books
19 April 1993, New York magazine, pg. 24, col. 2:
Now that New York has done such a fine job of documenting the “politically correct” phenomenon, perhaps it’s time to do the same for the scary, new out-of-control wave of “gotcha” journalism.
   
8 September 1996, New York (NY) Times, “Politics: Big Names and Big Money” by Michael Winerip, pg. 26:
“There is this gotcha journalism—any mistake, any flip-flop, any miscue is going to be amplified.”
(Dan Quayle—ed.)
 
Google Books
The Language of Journalism:
Profanity, obscenity & the media
By Melvin J. Lasky
New Brunswick, NJ: Transaction
2004
Pg. 65:
At best it is classified as an embarrassing work which attempts to give new impetus to what the Columbia Journalism Review terms “gotcha” journalism.*
*“Gotcha!” is a tabloid coinage, most memorably used by the London tabloids during the Flaklands War between britain and Argentina (1982). In the full-page headline of the Daily Mirror when a Royal Navy submarine unceremoniously sank an Argentinian ship, the Belgrano, with all 500 hands aboard….Gotcha! the front page screamed and, alas, all readers got it.