BRUSSELS >> The whole operation took less than 10 minutes. Three people drove a van up to Belgium’s main forensic storehouse at 2 a.m., cut through a perimeter fence, smashed the ground-floor windows, and placed bottles of accelerant inside.

The fire they set destroyed much of the nation’s chief forensic laboratory, including its entire cache of hair samples and thousands of other pieces of evidence critical to the prosecution of hundreds of criminal and terrorism suspects.

The Aug. 29 arson, in which no suspects have been publicly identified, has cast the troubled criminal justice system of this tiny country — the biggest per-capita exporter of foreign terrorists in Western Europe — into even deeper turmoil.

It has also added to mounting concerns about Belgium’s weak security systems, including at its nuclear sites. The country was used as the base to plot the attacks in Paris in November and was then itself hit by attacks in March that killed 31 people in Brussels at the international airport and on the subway.

Belgium’s ability to prosecute hundreds of criminals and terrorists may now be severely impeded, say justice officials, who have only reluctantly begun releasing information about the extent of the damage.

Prosecutors and lawyers fear that all the cases in which DNA evidence has been used may encounter difficulties during trials. That includes many of the 400 terrorist investigations, including about 15 related to the Paris and Brussels attacks.

The full extent of the troubles may not be known until the cases start coming to trial next summer. For now, prosecutors say they have not yet been made aware of cases in which evidence has been lost.

Sebastien Courtoy, a Belgian lawyer who specializes in defending terrorism suspects, said, “Of course, prosecutors are not going to come out with it themselves that evidence is lost.” He said that in some cases, his clients were fighting allegations based solely on forensic evidence, and that he would be “requesting to see the evidence.”

The staff at the lab has yet to complete a full inventory, said Jan De Kinder, director of the National Institute of Forensics and Criminology, or NICC as it is known by its acronym in Dutch. But he said six of 10 research laboratories were severely damaged and estimated that thousands of pieces of physical evidence were lost in the fire.

The bulk of the evidence was already analyzed and digitized and stored on a computer server not on the site, he said. But justice officials say it is not clear if the courts will accept digitized evidence alone if the physical evidence is destroyed.

According to the Brussels prosecutor’s office, it is up to a judge to determine whether a digital copy of a lost piece of physical evidence has the same value. “So far this has never posed any problems,” said Ine Van Wymersch, a spokeswoman for the Brussels prosecutor’s office, which is handling the criminal investigation of the arson.

But Thierry Werts, a spokesman for the federal prosecutor, acknowledged that the crime lab has “thousands and thousands of forensic evidence pieces” from terrorism investigations, including from the Paris network. “If they’re completely destroyed, then that can be troublesome for all of our cases that are concerned,” he said. “If they’re only in part destroyed, then we’ll have to redo the analysis.”

Courtoy pointed to a number of terrorism cases that could potentially be affected. One involves his client Mehdi Nemmouche, who has been charged in an attack on the Jewish Museum in Brussels in 2014. His DNA was found at the museum, the authorities say, and was stored at the lab.

Another is that of Mohamed Abrini, the so-called man in the hat at the airport bombing, who is suspected of having participated in the Paris and Brussels attacks. His DNA was found in most of the hide-outs in Brussels, the authorities say.

And then there is the case against Yassine Atar, a suspected member of the Brussels terrorist network who authorities say helped hide Salah Abdeslam, a suspect in the Paris attacks who was captured after an intensive three-month manhunt. Nitrogen that could be used in making bombs was found on Atar’s hair and his beard, the authorities say, samples of which were sent to the lab for analysis.

Abdeslam was extradited to France this year, and his case may not be affected by what was lost in the fire because he will be prosecuted there, and much of the evidence was gathered in France. Still, Abdeslam’s Belgian lawyer, Sven Mary, expressed consternation at the lack of security at a government facility housing the forensic evidence of thousands of cases.

Mary said in a telephone interview that the destruction of evidence at the lab posed “an enormous problem” for the Belgian justice system. “How can a defendant demand a second opinion of forensic evidence that doesn’t exist anymore?” Mary said.

The Brussels prosecutor’s office has yet to identify any suspects. But Brice De Ruyver, a professor in criminology at Ghent University, said “this looks more like gangsters from the organized crime world” than terrorists.

But officials and experts noted that the line between Belgium’s criminal and terrorist networks is increasingly blurred. They have been critical of the lack of security around a lab that handles thousands of cases a year for the federal police and the Belgian intelligence services.

On the night of the attack, security at the site consisted of a fence and video cameras. There was no active security on site, said De Kinder, the institute’s director.

Security appears to be even worse at private research laboratories that the government also depends on.

On the night of March 16 of this year, an arson attack was committed against a DNA laboratory in Charleroi, destroying evidence. The same lab was also attacked in 2001 and 2003, when it was destroyed and then rebuilt. The DNA laboratory of the Ghent University, which also does forensic research, was attacked in May 2005.

The latest arson attack puts Belgium’s security measures under renewed scrutiny, particularly at its nuclear sites. The series of attacks since March has prompted worries that terrorists are seeking to attack, infiltrate or sabotage nuclear installations or to obtain nuclear or radioactive material. Last year, the authorities seized surveillance video of a high-ranking Belgian nuclear official from the apartment of a suspect linked to the Paris attackers.

Belgium’s nuclear facilities have a record of breaches, prompting warnings from Washington and other foreign capitals. In 2013, two people scaled the fence at a Belgian research reactor, broke into a laboratory and stole equipment. In 2014, an unidentified person walked into a plant, turned a valve and drained 65,000 liters of oil used to lubricate reactor turbines, knocking the reactor out of commission for five months. And this year, the computer system of the country’s nuclear agency was hacked and shut down briefly.

According to the board of the European Network of Forensic Science Institutes, which counts 66 members in 36 countries, no international guidelines exist for providing security at forensic research institutes.

“Security procedures are based on national regulations,” the board stated. Addressing the arson in Belgium, the board said European forensic cooperation “ensures continuity of forensic services after any incident.” But it added that after this “regrettable incident,” security should be “reassessed.”

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