The scene is unfortunately familiar – ambulance crews rushing toward a shattered bus, police officers establishing a safe perimeter, TV crews capturing it all and sending their reports around the country and the world.

Despite the familiarity, however, it is too soon to draw many specific conclusions about Wednesday’s terror attack in Jerusalem. Whether this is the start of a new wave of attacks, a reaction to the exchange of fire in and around Gaza, the work of familiar players, or a small group of “selfstarters” will become clear in the days to come. In the meantime, it is worth examining recent patterns of terrorist activity.

Aside from determining who is responsible for the attack, the primary question is why now? Determining the answer, though, is not as straightforward as it might seem. For example, while Jerusalem had not experienced a suicide bombing since 2004 (Wednesday’s incident was not a suicide attack), and there have been no such attacks anywhere in Israel since 2008, the quiet the country has enjoyed in recent years has been illusory. According to the most recent statistics, there were 36 planned suicide bombings in 2009, an average of one every 10 days. Were it not for the vigilant efforts of the security services, including those of the Palestinian Authority, scenes like Wednesday’s – and worse – would be much more common.

It is tempting to link Wednesday’s attack to the recent intensification of activity in the Israeli- Palestinian arena: the stabbing attack in Itamar, the detention of Palestinian engineer Dirar Abu Sisi, last weekend’s heavy barrage of mortar fire, rocket attacks last month and this week on Beersheba, Ashdod and Ashkelon, the firing of missiles at IDF tanks around Gaza, and the IDF’s responses to these events using small arms, mortar and tank fire as well as airpower, which have cost the lives of both Palestinian terrorists and civilians, including children. Vigilantes have thrown their hat in the ring as well, through a series of “price-tag” actions.

NEVERTHELESS, IT is unlikely that the bombing in Jerusalem was either planned or carried out by the same groups or people responsible for the rocket and mortar fire in the South.

Given the size and type of device reportedly involved, it is more likely the same terrorist cell that was behind the planting of a pipe bomb on a traffic island in Jerusalem on March 6, which cost a municipal sanitation worker his hand.

All the major terrorist attacks in Jerusalem in 2008 – the active shooter attack at Mercaz Harav Yeshiva in March, the two bulldozer attacks in July, and a driver who plowed into a crowd of pedestrians in October – were carried out by residents of east Jerusalem. Despite the arrest of two Palestinian Islamic Jihad members by the PA security services in Jenin on Thursday, it could be that a small, local cell, with little or no connection to Hamas or Islamic Jihad, is now operating in the city.

Small cells have an advantage in terms of maintaining secrecy, which could explain why there reportedly were no intelligence warnings in advance of Wednesday’s bombing.

Further supporting this assessment is the fact that while Hamas and Islamic Jihad have taken responsibility for this week’s rocket and mortar fire, neither has done so for the Jerusalem bombing, at least not yet. On the contrary, an Islamic Jihad spokesman denied responsibility – while applauding the attack.

A possible connection between Wednesday’s attack and the recent escalation with the groups in Gaza might be more inspirational than operational. In light of the response to the rocket and mortar fire, especially the resultant – however inadvertent – deaths of civilians, the Jerusalem cell might have felt the time was right to put an already planned attack in motion.

Small cells, individual terrorists, or mere bad luck can play a big role in the back and forth between Israel and its rivals in Gaza, and can push both sides, despite their reluctance to continue this dangerous tango, into a period of continuous, mutual bloodshed.

Jonathan Schachter is a research fellow and Yoram Schweitzer is the director of the Program on Terrorism and Low Intensity Conflict at the Institute for National Security Studies at Tel Aviv University.