A mystery benefactor has offered $30m (£18.4m) bounty for information on whom shot down the Malaysia Airlines flight MH17 in eastern Ukraine last July.

The bounty was offered to Wifka, a Germany-based fraud investigation company, to prompt anyone to come forward who has information about who brought down the aircraft, which was carrying 298 people from Amsterdam to Kuala Lampur.

The mystery client has also offered a new identity to any informant.

Josef Resch of Wifka told German finance magazine Capital that one of the middlemen spoke in a Swiss accent.

He added he's confident the offer is real as the money is already on deposit in a Swiss bank in Zurich and he received an advance payment of €40,000 (£24,000, $51,567) for his services.

Speculating about the possible identity of the client, Resch said it could be a Russian oligarch who wants to damage Russia's President Vladimir Putin.

The plane crashed in pro-Russia rebel-held city of Donetsk, 40 km from the border with Russia. Western intelligence agencies believe the aircraft was shot down by the rebels with a surface-to-air missile supplied by Russia.

Resch added he was not ruling anyone out, not even intelligence agencies.

Wifka said in an online statement that after the plane crashed "all political parties, at home and abroad, said they owed it to the victims, their families and the public to clarify the circumstances of the crash and present evidence for what happened. None of this has yet been done."

A preliminary report by the Dutch Safety Board (DSB) into the crash ruled out technical faults or actions by the crew. It said the plane broke up in the air due to "a large number of high-energy objects" that penetrated it from the outside.

Biggest bounties in history

The mysterious offer is the biggest bounty ever.

The second-largest sum of money given for this purpose amounted to $25m (£15.3m), offered by the US in 2001 for information about Osama Bin Laden's whereabouts.

German-Finnish internet entrepreneur Kim Dotcom offered $5m for information to prove the US government acted illegally when assembling a copyright infringement case against him in 2012.

Conservative NGO Voters Trust, offered $1m bounty for "smoking gun" information proving the IRS or members of the Obama administration targeted Tea Party affiliated groups.

Bounty Hunter website recently offered $16,891 (£10354) to catch whoever hacked into the email accounts of Satoshi Nakamoto, the fabled creator of bitcoin and Roger Ver, a bitcoin investor.