German and Swiss authorities have confiscated documents from private detective Josef Resch, who has been conducting his own investigation of the 2014 crash of Malaysia Airlines Flight 17, Dutch officials and media said Tuesday.

Investigators believe that some of the documents seized after last week's raid on the detective's home in Bad Schwartau, northern Germany, may shed light on the circumstances of the tragedy. Some of the papers are said to be "explosive" and could help determine the culprits.

According to De Telegraaf daily, the German detective began his own probe two months after the catastrophe, and has received some $19 million for his investigations. His generous clients remain unknown.

"We are hoping to get some information about this. That's why the raids at his home were carried out," the spokesman for the prosecution service, Wim De Bruin, told AFP.

The contents of Resch's safe-deposit box in a bank in Zurich, Switzerland, were also inspected.

"We don't actually know what was in the box. The Swiss judge must now decide if its contents can be handed over to Dutch officials," the spokesman said.

He added that it is possible that the detective may have been in contact with the culprits.

The Boeing 777 aircraft, operated by Malaysia Airlines as Flight 17, was en route from Amsterdam to Kuala Lumpur when it was struck by a BUK anti-aircraft missile while flying at 33,000 feet over war-torn eastern Ukraine on June 17, 2014. All 298 passengers and crew — the majority of them Dutch — died in the crash.

A criminal investigation is ongoing in the Netherlands to identify who fired the missile and where from, although many believe that those responsible will never be brought to justice.

The first official findings by criminal investigators are expected after the summer, as they await further information from Russia.