Mastenbroek had worked for SARS and was later appointed to the Kroon Advisory Committee set up by Finance Minister Nhlanhla Nene to investigate the allegations the Sunday Times published about the rogue unit.
He was also formerly married to Phylicia Oppelt, who was the editor of this newspaper when the stories were run.
Joubert's claims have been widely reported and have called into question the veracity of the Sunday Times' stories.
The matter is before the press ombudsman and the Sunday Times says it respects his authority and this process - including the appeal process - but that the newspaper would like to set the record straight regarding the issues raised by Joubert, which are not necessarily the substance of the complaint.
Joubert says Mastenbroek was biased towards two former senior SARS officials at the centre of the rogue unit scandal, Johann van Loggerenberg and Ivan Pillay.
She also implies that Oppelt's objectivity was compromised by her personal relationship with Mastenbroek, which caused her to abuse her position as editor to push his agenda in this newspaper.
The Sunday Times says that nothing could be further from the truth - and there is documentary evidence to prove it.
Joubert first tried to get the Sunday Times to pursue Pillay and Van Loggerenberg in August 2013 after she had spoken to a source, whom she this week revealed to be Mastenbroek.
In an e-mail sent to a member of the Sunday Times' investigations unit on 5 August 2013 at 8.59pm, she says Pillay is "not straight" and "does the dirty".
Joubert goes on to say Pillay has "his own man who is literally doing all his bidding: Johann van Loggerenberg". She calls Van Loggerenberg an "old security man. Very close to [former police chief Jackie] Selebi (Selebi had particular liking for those old Bantustans cops and security types)."
The unit member responded by cautioning her to investigate these claims thoroughly before lending them any credence.
"Woaah, steady on!" her colleague warned. "We'd need to do a very thorough drilling down of who the sources are and if they aren't just circulating the same planted stuff for their own agendas."
Joubert agreed: "Obviously. Now have to start looking for evidence! That's what I'm doing. I was just telling you what I'm keen to start looking at."
Nothing much came of it. But three months later, in November 2013, Joubert was investigating links between Radovan Krejcir and Western Cape gangsters and businessmen under investigation by SARS.
SARS was refusing to co-operate with her and she asked members of the investigative unit for help. Sunday Times says its sources at SARS told them they wouldn't talk to her off the record because she "couldn't be trusted", but that the paper had naively told them: "Trust her. She's one of us."
Soon afterwards, based on Sunday Times' assurances, Joubert gained access to one of the newspaper's sources.
Around the same time, Business Times reporter Malcolm Rees was investigating shenanigans in the tobacco industry and stumbled on the ill-fated love affair between Van Loggerenberg and Belinda Walter, a Pretoria lawyer representing several small tobacco companies.
Walter, while on the payroll of the State Security Agency to spy on her clients, claimed she had uncovered evidence Van Loggerenberg was spying illegally on her and other taxpayers.
She lodged a complaint to this effect with SARS and the inspector-general of intelligence.
However, independently of Rees, Piet Rampedi and later other Sunday Times reporters were gathering evidence of members of SARS spying illegally on taxpayers.
Oppelt decided it made sense to pool the reporters' efforts.
The paper says that at no point, however, was Joubert involved in this investigation, so perhaps it is understandable that she didn't know who the real sources for the story were.
It says that its reporters had access to more than a dozen sources comprising former officials or agents of SARS, the intelligence services, the Treasury and police. Mastenbroek was not one of them.
Apart from detailed information Sunday Times reporters were able to cross-check with other sources, they supplied the newspaper with piles of internal memos, transcripts of voice recordings, WhatsApp and BlackBerry messages, and the real clincher: sworn statements in which SARS officials admitted bugging the National Prosecuting Authority offices.
Walter's complaint and the Sunday Times' stories led to a number of investigations. The first independent probe was headed by respected advocate Muzi Sikhakhane. It confirmed the existence of the rogue unit.
Next came the finance minister's advisory panel, this time headed by a respected retired judge, Frank Kroon, who confirmed SARS had broken the law in setting up the rogue unit and that it had committed unlawful acts.
Finally KPMG, one of South Africa's top audit firms, made the same finding.
The Sunday Times says it goes without saying that it could influence neither the finance minister's choice of advisers, nor the outcome of the three independent investigations that confirmed SARS officials spied on taxpayers.
Perhaps Joubert actually believes the Sunday Times was used to further her source's agenda. But the evidence, when looked at dispassionately, proves otherwise.
The Sunday Times says it did everything by the book, and stands by its stories.
Source: Sunday Times via I-Net Bridge
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