On Tuesday, a lone gunman threw at least three grenades into a bustling square in Liège, Belgium, then opened fire with an automatic weapon, killing at least four people and wounding at least 122 more. Officials identified the killer, who died during the attack, as Nordine Amrani, 33, a Belgian of Moroccan descent with a criminal background. European Union President Herman Van Rompuy echoed the sentiment of many Belgians when he said, "Faced with the inexplicable, I am perplexed, I am horrified." Here, a concise guide to what we know about these "atrocious murders":

What happened Tuesday?
Amrani carried a bag containing up to a dozen grenades, a handgun, and a Belgian-made FAL automatic rifle into Liège's central Place Saint-Lambert, site of an annual Christmas market. According to witnesses, he climbed onto the roof of a popular bakery, lobbed three or four grenades toward a busy bus stop in the square below, then randomly fired into the crowd with the automatic rifle. Amrani then lost his own life, either by shooting himself in the head or by triggering one of his grenades. A number of grenades were left in his sack when he died.

Who are his victims?
The dead include a 17-month-old child, two teenage boys, and a 75-year-old woman. Several other victims of the attack are still in critical condition. Police say that earlier Tuesday, Amrani also murdered a woman — reportedly a neighbor's cleaning lady — and stashed her body in a warehouse where he grew marijuana.

What do we know about Amrani?
A welder by trade, Amrani was an authority on weapons, able to build and repair firearms of all sorts. He was on parole after serving a 58-month sentence for illegal possession of 10 firearms, 9,500 weapons parts, and 2,800 marijuana plants. His long rap sheet also included convictions for pimping and selling stolen goods. "We'd never observed that he had any mental problems," said city prosecutor Danièle Reynders. "He has no history of terrorist acts."

So it wasn't terrorism?
An early report, sourced to Pakistan's Karachi Post and picked up by several U.S. blogs, suggested that Amrani was taking revenge for a Belgian court's conviction on Monday of four family members for the "honor killing" of a Muslim woman who had chosen to live with a Belgian man rather than marry a Pakistani cousin. "Given the timing of the attack and where it was carried out, this certainly cannot be discounted," says Aaron Goldstein at The American Spectator. Oh please, says Charles Johnson at Little Green Footballs. Amrani "was a drug dealer, not a jihadi, and there’s no indication that he was even a practicing Muslim."

So what prompted this massacre?
Police say Amrani didn't leave a note. However, Amrani was due at the police station that afternoon for questioning over an undisclosed vice charge, suggesting perhaps "that his attack was some sort of desperate final lashing out," says James Kanter in The New York Times. The new charges were not "particularly serious," adds Amrani's lawyer, Jean-Francois Dister, but "he was afraid of being taken into custody." It's not clear if the mass shooting was premeditated, but before the incident, Amrani transferred money to his wife's bank account with the message: "I love you my love. Good luck."

Sources: American Spectator, BBC News, Businessweek, Little Green Footballs, New York Times, RT, Telegraph