On April 15 Detective Inspector Andrea Power of Weymouth CID said: "An investigation is currently underway to establish the cause and the circumstances around the blaze. We are treating the fire as suspicious"
Dorset Police subsequently announced the arrest on Wednesday of a 68-year-old Beaminster man and two days later said the suspect had been released "under investigation."
No bail conditions are believed to have been imposed.
The force has refused to confirm the identity of the man but a spokesman for Austrian-born financier Treichl, 68, who has owned the property since 2001, told The Sun: "Mr Treichl is helping police with their inquiries. He wants to resolve this as much as anyone.
"He and his family are devastated at the loss of the house."
Treichl's father Heinrich Treichl, whose mother was a baroness, was a former general manager of the now-collapsed Austrian bank Creditanstalt.
Michael Treichl, who holds an MBA from Harvard Business School, is a founding-partner of London-based hedge fund Audley Capital Advisors. His office could not be reached for comment on Saturday.
Before that, he co-founded Bessemer Vogel & Treichl, the European arm of a £3.9 billion private equity fund.
Near-neighbour Derek Horton, who works on the Parnham estate, told The Telegraph that an extensive investigation had been carried out following the blaze.
He said: "Everyone who works here has been questioned by the police and the fire brigade."
Treichl and his wife Emma, 54, purchased the property in 2001 from furniture designer John Makepeace, and moved into the property along with their four children.
Their extensive remodelling of the building was the subject of a 2009 article in Dorset Life in which Emma Treichl said: "The children enjoy the atmosphere of suits of armour and endless games of hide and seek, and a house needs to be lived in for it to feel like a home and not a museum.
"We smoothed out the corners a little, but didn't dent Parnham's considerable history."
The property's halls and reception rooms played host to a menagerie of game trophies collected by Mr Treichl, who is reported to be an enthusiastic shot telling one interviewer he took aim at "everything that flies" in England.
One magazine reported that a polar bear and a lioness were among the taxidermied inhabitants of Parnham House.
The driveway featured a life-sized statue of the Greek goddess of youth, Hebe, and inside the house, suits of armour on high plinths stared down at visitors.
Much of the current design of the building is owed to Regency architect John Nash, who worked on the 19th Century enlargement of Buckingham Palace.
His work on Parnham, commissioned by then-owner Sir William Oglander in 1810, can be recognised in the distinctive winding staircases and stone mullioned windows.
However the oldest parts of the building dates back to 1522m when a home which then stood on the site was rebuilt from the ground up, for Robert Strode.
The Strode family remained in occupation until 1764 when the male line failed.
On 5 July 1645, while protecting house and home, Lady Strode was brutally killed by a soldier under the command of Roundhead commander Colonel Fairfax.
