Before the war Brzica was a scholarship student at the Franciscan college of Široki Brijeg in Herzegovina and a member of The Great Brotherhood of Crusaders, an organization part of the Croatian Catholic movement. He spent some time studying law in Zagreb where he became the Ustashe Youth member and later a member of the Croatian fascist Ustaša government (1941-45) and one of the guards in the Jasenovac concentration camp.
As an Ustashe he held the rank of Lieutenant. While he is known for having beaten an inmate to death in March 1943, he is notorious for having won a contest in which he used a curve-bladed knife, also called a srbosjek, to kill newly arrived concentration camp prisoners. Brzica boasted of winning the contest by killing the largest number of prisoners - 1,360 people. Some other sources set Brzica's "record" at a lower number, between 670  and 1,100.
- Bulajić 2002, p. 215.
- Friganović's comments in full:
"“Franciscan Pero Brzica, Ante Zrinušić, Sipka and I waged a bet on who would slaughter more prisoners that night. The killing started and already after an hour I slaughtered much more than they did. It seemed to me that I was in seventh heaven. I had never felt such bliss in my life. And already after a few hours I slaughtered 1,100 people, while the others only managed to kill 300 to 400 each. And then, when I was experiencing the greatest ecstasy I noticed an elderly peasant standing and peacefully and calmly watching me slaughter my victims and them dying in the greatest pain. That look of his shook me: in the midst of the greatest ecstasy I suddenly froze and for some time couldn't make a single move. And then I walked up to him and found out that he was some Vukasin [Mandrapa] from the village of Klepci near Capljina whose whole family had been killed, and who was sent to Jasenovac after having worked in the forests. He spoke this with incomprehensible peace which affected me more than the terrible cries around us. All at once I felt the wish to disrupt his peace with the most brutal torturing and, through his suffering, to restore my ecstasy and continue to enjoy the inflicting of pain.
“I singled him out and sat him down on a log. I ordered him to cry out: ‘Long live Poglavnik [Fuehrer] Pavelić!', or I would cut his ear off. Vukasin was silent. I ripped his ear off. He didn't say a word. I told him once again to cry out ‘Long live Pavelić!' or I would tear off the other ear too. I tore off the other ear. ‘Yell: “Long live Pavelić!”, or I'll tear off your nose.' And when I ordered him for the fourth time to yell ‘Long live Pavelić!' and threatened to take his heart out with a knife, he looked at me, that is, somehow through me and over me into uncertainty and slowly said: ‘Do your job, child.' [Radi ti, dijete, svoj posao.] After that, these words of his totally bewildered me. I froze, plucked out his eyes, tore out his heart, cut his throat from ear to ear and threw him into the pit. But then something broke within me and I could no longer kill that night ... Brzica won the bet because he had slaughtered 1,360 prisoners and I paid the bet without a word.” (Qtd. in The Role of the Vatican in the Breakup of the Yugoslav State, by Dr. Milan Bulajić, Belgrade, 1994: 156-57; from a January 1943, interview with Friganović by psychiatrist Dr. Nedo Zec, who was also an inmate at Jasenovac.)
-  Archived 2016-05-03 at the Wayback Machine.
- Siniša Ivanović, Špijun u mantiji, Nova knjiga Belgrade, 1987, p. 78
- "Sećanja Jevreja na logor Jasenovac" by Dušan Sindik, Savez jevrejskih opština Jugoslavije 1972, p. 154
"Then the Ustashe butchers came: Ljubo Miloš along with a wolfhound and Ustashe lieutenant Pero Brzica who started from the left flank of the human formation/interrogating what were the occupations of these people."
- State Commission[page needed]
- State Commission, p. 50
- Jasenovac and the Holocaust in Yugoslavia by Barry M. Lituchy Jasenovac Research Institute (1st edition), New York (2006):
"Another historian, Teophilo Gardini, reports a very strange contest of "Serbian throat-cutting" - won on August 29, 1942 by a certain Petar Brzica, a former Franciscan of the Široki Brijeg Monastery"
- Dr. Nikola Nikolic testimony, see Avro Manhattan's Vatican's holocaust, p. 48
- Taborišče smrti - Jasenovac by Nikola Nikolić (author), Jože Zupančić (translator), 1969, p. 293
- The Role of the Vatican in the Breakup of the Yugoslav State, by Dr. Milan Bulajić, Belgrade (1994), pp. 156-57: a January 1943 interview with Ustaša Mile Friganović by psychiatrist Dr. Neđo Zec, who also had been an inmate at Jasenovac
- The Glass Half Full by Alan Greenhalgh, p. 68 (ISBN 0977584410)
"Wherever they went they experienced similar cruelty from the Ustashe guards. They heard stories about the fierce butcher, Petar Brzica, who boasted that during one night alone he killed 1,360 prisoners."
- Bulajić 2002, p. 215
- Taborišče smrti-Jasenovac by Nikola Nikolić (author), Jože Zupančić (translator), 1969, p. 293
Tisto noč je ustaš Pero Brzica v hitrosti in spretnosti svojega krvniškega posla prekosil vse ustaške klavce. Sam je namreč zaklal 670 internircev jasenovškega taborišča. Med seboj so tekmovali v klavskem poslu Brzica, Bonzo, Šipka, Zrinušić in še nekaj drugi klavci, ki pa so za Brzico znatno zaostajali
- C.I. Christian, "Nedjelja", Zagreb, 19 October 1942, referenced in Sângeroasa destrămare: Iugoslavia by C.I. Christian, Editura Sylvi (1994), p. 170 (ISBN 9739175015, ISBN 978-973-9175-01-2)
- Bulajić, Milan (1994). The Role of the Vatican in the break-up of the Yugoslav State: The Mission of the Vatican in the Independent State of Croatia. Ustashi Crimes of Genocide. Belgrade: Stručna knjiga.
- Bulajić, Milan (2002). Jasenovac: The Jewish-Serbian Holocaust (the role of the Vatican) in Nazi-Ustasha Croatia (1941-1945). Belgrade: Fund for Genocide Research, Stručna knjiga.
- Crimes in the Jasenovac Camp. Zagreb: State Commission of Croatia for the investigation of the crimes of the occupation forces and their collaborators. 1946.