* Winterkorn is CEO at VW's controlling shareholder
* Also holds key positions at Audi, Scania, trucks unit
* Winterkorn resigned last week to give VW a "fresh start"
By Andreas Cremer
BERLIN, Oct 1 (Reuters) - Martin Winterkorn, the former boss of Volkswagen who quit last week saying he wanted to give the German carmaker a "fresh start" to tackle a scandal over rigged vehicle emissions tests, remains in four key positions involved with the group.
The 68-year-old is chief executive of Porsche SE , the family-owned holding company that controls a majority stake in Volkswagen, as well as chairman of VW's flagship luxury brand Audi, trucks division Scania and the group's newly-created Truck & Bus holding.
The longer Winterkorn stays on in the background, the harder it will be for the company to convince critics it can move on from the biggest business crisis in its 78-year history, according to some investors and analysts.
"It's a real surprise that Winterkorn is still there," said Ferdinand Dudenhoeffer, head of the Center of Automotive Research at the University of Duisburg-Essen.
"VW has pledged a fresh start but his continued presence is detrimental to VW's public image."
Volkswagen declined comment on Winterkorn's positions within the group, saying it was up to the supervisory boards of the brands in question to take any decision about his future.
A source close to the company said Winterkorn had not yet quit his group positions because investigations were underway and a hasty withdrawal could be seen as an admission of guilt.
German prosecutors are conducting preliminary investigations into Winterkorn as part of a probe into the company following allegations of fraud from unidentified people. They said on Thursday they had no evidence against Winterkorn and he was not under formal investigation.
Volkswagen's supervisory board said last week Winterkorn "had no knowledge" of emission test manipulations. Severance is forfeited if the board decides his employment was ended for a reason for which he was responsible, the company's annual report says.
After almost nine years as CEO, Winterkorn has a pension pot of 28.6 million euros ($32 million) and could get millions more in severance depending on how the supervisory board rates his departure.
Under certain conditions, Winterkorn could collect severance equal to two years of annual compensation, the annual report says, without specifying whether this refers to fixed remuneration or also includes variable compensation.
Volkswagen declined to comment on whether Winterkorn, whose total compensation package came to 16 million euros last year, can expect a departing bonus or share options.
Volkswagen's unusual structure harks back to the ill-fated attempt by sports-car maker Porsche in 2008-2009 to acquire the much-bigger automaker.
Helped by Porsche's mounting financial problems at the time, Volkswagen turned the tables and ultimately bought Porsche, with Winterkorn also taking the helm of Volkswagen's controlling shareholder -- the Porsche SE holding company.
Volkswagen's new CEO Matthias Mueller "must now get the full support of the supervisory board to be able to clear up the (emissions) disaster and finally overhaul old, entrenched structures at VW," said Ingo Speich, a fund manager at Union Investment which holds about 0.4 percent of Volkswagen preference shares.
"That's why it's crucial that Martin Winterkorn will also pull out of the influential Porsche SE holding. Otherwise, there can be no credible elucidation (of the scandal)."
$1 = 0.8951 euros Editing by Mark Potter