They are both Arabs who lived in East Jerusalem with blue Israeli identity cards. One committed the massacre at the Mercaz Harav Yeshiva in March, gunning down eight teenage students. The other rampaged through downtown Jerusalem on Wednesday with a bulldozer he stole from a construction site. Wednesday's attacker, Husam Taysir Dwayat, was a 30-year-old father of two from Sur Bahir. The gunman who massacred the Mercaz Harav students came from the nearby neighborhood of Jebl Mukaber. Both attackers are examples of the type of terrorism threat that Jerusalem now faces. The city has experienced a lull in terrorist attacks over the past couple of years in comparison to 2001-2004, when there were suicide bomb attacks every few months. While Jerusalem has known the occasional terrorist stabbing over the past few years, before Mercaz Harav, the last major attack in Jerusalem was in September 2004 when two border policemen were killed and 17 civilians wounded in a suicide bombing by a female terrorist at the French Hill junction. But since then, the IDF Central Command and the Shin Bet (Israel Security Agency) have been very effective in preventing terrorist infiltrations into Israeli cities. This is not due to a drop in Palestinian attempts, but it has to do with the near-completion of the West Bank security barrier and IDF operational freedom throughout the territories. In 2007, there was only one suicide bombing in Eilat and so far this year, just one in Dimona. The Shin Bet and the Israel Police launched a joint investigation Wednesday into the bulldozer attack, and while the possibility that Dwayat acted alone seems the most likely, other options have yet to be ruled out. Dwayat was known to police for previous criminal activity, and defense officials raised the possibility that he had been coerced by terrorist elements to perpetrate the attack. It would not be the first time, the officials stressed, that terrorism and crime went hand in hand. On the other hand, there is also the possibility that Dwayat had a falling-out with his employers at the Jerusalem light rail construction site, or that he decided on his own to perpetrate the attack on behalf of his brethren in the Gaza Strip. Whatever the case may be, the Shin Bet did not record a terrorism threat prior to the attack. According to security officials, the IDF in the West Bank and the Shin Bet are currently operating against five warnings of Palestinian terrorist groups that are working to perpetrate an attack inside Israel. This is further evidence that the attacker likely acted alone and of his own accord. The same was the case with the Mercaz Harav attacker, who also acted alone, and while he had a submachine gun - possibly provided to him by handlers - in a country like Israel where a large number of citizens have guns at home, it is fairly easy to buy weapons on the black market. What makes the possibility of foiling such attacks even more difficult is the fact that both Dwayat and the Mercaz Harav gunman carried Israeli ID cards allowing them to travel freely throughout Jerusalem and the rest of the country. In the case of Mercaz Harav, one might argue that security forces should have caught the gunman since he was carrying a weapon, but in Wednesday's attack Dwayat was unarmed and used a bulldozer, which can be found these days on almost every street corner in Jerusalem. The security fence would also not have helped in such a case. With blue ID cards, the two attackers would have easily crossed into Israel like the thousands of blue card holders who live in the West Bank and travel to Israel daily. From a security perspective, these types of attacks are the most difficult to foil. There is no planning, no infrastructure and rarely any accomplices.