As Miriam and Emmanuel Riva were laid to rest Tuesday in Tel Aviv, Belgian police and security service, aided by Israeli agencies, continue its investigation into the terror attack that took place at the Jewish museum in Brussels last Saturday. But the mystery surrounding the affair is only growing.Most experts believe that the terror attack was the work of a professional. Images caught by a security camera, and that the Belgian police have released for publication, show the assassin entering the museum in a well calculated manner, carrying a knapsack.He pulled out a Kalashnikov assault rifle and opened fire at short range. Following the shooting, he walked out of the museum and onto the sidewalk, without breaking into a run and with no sign of panic.Unlike what earlier reports indicated, the gunman was not assisted by a driver of a getaway car.The person who was arrested after the shooting believed to be the driver of a getaway car is no longer a suspect, but a witness.The Belgian investigators seem to believe that there was no getaway care and the assassin walked away on foot. Yet it is possible that he was assisted by unknown persons, who may have provided him with the weapon.As the gunmen left no traces – neither fingerprints nor other clues – the investigators are focusing on the security cameras’ footage.Thousands of hours of recordings from private cameras and public cameras in a wide perimeter around the Jewish Museum – including in the subway and railway stations – are analyzed with the hope that they may shed a light and direct the police toward the right path.According to the Belgian Police, the assassin likely wore a miniature camera on his shirt to record the murder, similar to that worn by the gunman who shot four people dead outside a Jewish school in Toulouse, France, two years ago.But for Belgian experts the crime is more reminiscent of what happened 25 years ago to Joseph Wybran. On October 3, 1989, Wybran, a Belgian immunologist and head of the umbrella organization of Belgian Jewish groups, was shot to death in the parking lot of the Erasmus Hospital of the Free University of Brussels, where he worked.At the time, an obscure Beirut-based organization, called Soldiers of the Right, claimed responsibility for the murder, but in 2008, a Moroccan-Belgian terrorist named Abdelkadder Belliraj purportedly confessed to it and a number of other political killings. The following year, a Moroccan court convicted him of a number of terror-related crimes and sentenced to him to life in prison, although by then he had claimed that his confessions were extracted by way of torture.In short, like the 1989 killing, this recent crime was the work of a professional and well-trained terrorist assassin.On the one hand, Norway and the US have in recent years witnessed psycho-terrorists who acted alone and in cold blood.And yet, there are of course professional and capable terrorist organizations such Hezbollah or al-Qaida that could be behind this operation.Since the assassination of Imad Mughneiyeh, Hezbollah’s “defense minister,” in 2008, in Damascus – attributed to the Mossad – the Lebanese Shi’ite organization has committed to avenge his death by attacks against Israeli or Jewish targets anywhere in the world.It has even had some successes, such as in New Delhi and in Burgas, Bulgaria, where a suicide bomber killed six Israeli tourists.If Hezbollah is behind the Brussels attack, it is unlikely that it will claim responsibility.However, it may leak hints – kind of a blink of an eye – of its involvement for domestic consumption to its trusted media outlets.Since the Second Lebanon War in 2006, Hezbollah’s revenge attacks against Israeli or Jewish targets all required the approval of its so-called boss, the Iranian intelligence, and more specifically, Gen. Qasem Suleimani, commander of the Revolutionary Guards’ Quds Force.Another even more likely possibility that must be taken into account is that the attack was carried out by an arm (locally organized in Belgium or abroad) of al-Qaida – that is to say, a cell of the Islamic Jihad, which seeks out attacks against Jewish and Israeli targets, whether instructed to do so from the higher ranks or a decision made by a small local cell, such as the shooting in Toulouse.Some Israeli journalists have tried to create the impression that the greatest mystery in this story is whether the murdered, certainly the two Israelis, were a deliberate target of the terrorist and whoever sent him, or just tourists who walked into the line of fire by chance.This impression is enhanced by the background biographies of the murdered Israeli couple.Emmanuel Riva was an accountant who more than six years ago worked for Nativ, the organization in charge of immigration from Russia and the Commonwealth of Independent States, a body that operates under the auspices of the Prime Minister’s Office.Nativ in the past was a member-organization of the intelligence community, but it ceased to be so more than a decade ago.What is as clear as day is that Emmanuel was not an intelligence officer and was certainly not involved in operations. He was a product of the Finance Ministry who was sent to work as an accountant for Nativ.He left Nativ at some point, and it is not clear what he did after that but I am certain that he did not work in the intelligence community or in the Foreign Ministry.He went abroad with his wife, Mira, who was also killed in the attack. She was assigned to the Israeli Embassy in Germany a few years ago. She too was an accountant in the Prime Minister’s Office.Media outlets in Israel have irresponsibly released heavy hints about her employment at the Prime Minister’s Office, which were quickly “translated” in the Belgian media as indications that she was a Mossad employee.Regardless, it must be emphasized that she was an accountant, who worked in an administration department, and was not an intelligence officer.Thus it seems very likely that a terror group would manage to identify her position and employer, follow her two years after she had finished her tour of duty, and kill her during a private visit to the Jewish Museum.As an accountant she should not be considered a high-value target. There are better Israeli targets for Hezbollah or al-Qaida, such as senior Israeli officers for example.At this stage it’s best to be careful and not to hasten to any definitive conclusions.Every investigative direction is possible in the field of terror. The chance is still great that the details of this attack were just a tragic coincidence in which an Israeli couple on a private tour of Brussels found themselves in the wrong place at the wrong time – when terrorists decided to attack a Jewish target.