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(CNN) -- He's known as the "bull dog" in South Africa's legal circles, and just days in to Gerrie Nel's merciless cross-examination of Oscar Pistorius, it's easy to see why.
The veteran state prosecutor's relentless grilling of Pistorius -- on trial for the murder of his girlfriend Reeva Steenkamp on Valentine's Day last year -- has riveted people around the world to their TV sets, and has sparked a debate about whether Nel's no-holds-barred tactics have crossed the line.
Nel had to wait weeks to take on Pistorius, but has wasted no time since he got the chance late on Tuesday. At various times Nel has called the 27-year-old a liar, implied that Pistorius was pretending to be too emotional to testify, reduced him to tears, and laughed at him for failing to recall the answer to one of Nel's questions as the prosecutor ruthlessly tore into various aspects of his testimony.
On Wednesday Nel took the defense by surprise when he played a video, taken just months before Steenkamp's death, of Pistorius shooting a watermelon at a firing range with friends and describing the impact as a "zombie-stopper."
"You know that the same happened to Reeva's head? It exploded," Nel told Pistorius, before showing the court -- and the multitudes around the world watching on live TV -- a grisly photograph of Steenkamp's wounded head, her hair soaked in blood and tissue from the impact of the bullet that tore through her skull.
"Have a look there," Nel barked, to gasps from the courtroom. "I know you don't want to because you don't want to take responsibility, but it's time that you look at it."
Pistorius, sobbing heavily, said, "I've taken responsibility but I will not look at a picture where I'm tormented by what I saw and felt that night. As I picked Reeva up my fingers touched her head -- I remember, I don't have to look at a picture, I was there."
Pistorius' family sat appalled at the front of the courtroom. The sprinter's attorney, Barry Roux, called Nel's tactics an "ambush" and objected. And the court adjourned for a recess, leaving a hysterical Pistorius to weep in the dock and shocked journalists and legal observers to debate what they'd just seen.
"It's not unusual for an accused to be shown pictures of the deceased. Although not always in this dramatic manner," tweeted Barry Bateman, an Eyewitness News reporter in the courtroom.
Did Nel overstep the bounds of decency in his interrogation of Pistorius? CNN legal expert Kelly Phelps says that while Nel's strategy -- to unnerve the accused and destabilize his version of events -- was valid, showing the world a bloody photo of Steenkamp was "unnecessary and gratuitous."
"Nel has a responsibility to protect the dignity of the deceased and the victim's family," Phelps said. "He could have showed Pistorius that photo without having to broadcast it for the whole world to see."
While Phelps said most people she spoke to shared that view, others said that Nel's ultimate responsibility to the victim and the family is to achieve justice. If that's how the prosecutor thinks he'll get a conviction, then he's right to pursue any avenues to get there, the thinking goes.
Nel has infuriated quite a few opposing lawyers over the course of his career, Phelps says, but he has long had a reputation for being incorruptible and impossible to intimidate. When he went after South African police commissioner Jackie Selebi in a corruption case in 2008, he was arrested in front of his family. He spent a few days in jail before being released -- and ultimately put Selebi behind bars. In his spare time, he's active in South Africa's amateur wrestling federation as a coach and official.
Nel may be known for being a courtroom bull dog, but is his bark worse than his bite? Despite his long assault on Pistorius' testimony, the fact remains that the state has very little evidence to disprove the track star's version of events that night.
"I think he knows that the state's case is mostly circumstantial, and it was always going to rely heavily on cross-examining Pistorius," Phelps said. "And while Nel's been successful in getting his narrative on the record, he hasn't yet been able to get Pistorius to support that narrative."
In other countries, Nel's almost theatrical approach might be able to sway some members of a jury, but South Africa doesn't have jury trials -- and Judge Thokozile Masipa has already reprimanded Nel several times when he stepped over the line in her view.
Ultimately Phelps says she doesn't expect the judge's decision to be affected by the prosecutor's flair for the dramatic.
"She's experienced enough to know the various tactics employed by the lawyers on each side," Phelps says. "She will have sat before them in court on many occasions, and she's well positioned to cut through the white noise."
"Still, it's never wise to get a judge's back up."
CNN Wires contributed to this report.