A week after the unsuccessful February 24th al Qaeda bombing attack on the Abqaiq oil facility, Saudi and Iraqi border patrols began to catch al Qaeda members fleeing into Iraq. This was expected, as Islamic terrorists have been moving back and forth for a long time. But these days, the normally empty desert border is heavily patrolled on both sides.
Apparently there was some very good coordination between the Saudi and Iraqi security organizations these days. Part of this has been due to Saudi complaints that al Qaeda fugitives have been finding refuge in Iraq. Actually, that's been going on for years, but was never a problem until al Qaeda began setting off bombs in Saudi Arabia. At that point, the "truce" between the Saudis and al Qaeda was over. This hurt al Qaeda more than the Saudis, because much, if not most, of the al Qaeda financing came from Saudis (either wealthy individuals, or charities). Once the bombs started going off, and Saudis got killed, the donations went down, and the Saudi government began making life difficult for Islamic charities, and wealthy donors.
Iraq was another matter. When Saddam was running things, there was someone the Saudi security people could call in Baghdad, if they were looking for a troublesome al Qaeda member believed hiding out in Iraq. It's only been in the last year that the Saudis have again found reliable people at the other end of the phone in Baghdad. The guy on the Iraqi end may be a stranger (a Shia or Kurd), as opposed to the Sunni Arabs who served Saddam. But now both Iraqi and Saudi security people have a common enemy with al Qaeda, which overrides religious and Ethnic differences (Kurds are not Arabs, but ethnically related to the Iranians and Europeans).
From the Summer of 2004, and into early 2005, al Qaeda terrorists wanted in Saudi Arabia were able to hide out in Iraq. While moving around in Iraq was dangerous, it was safer than trying to hide out in Saudi Arabia, among a populations enraged at al Qaeda attacks. But al Qaeda attacks in Iraq were having the same impact in Iraq. Despite the anger among Iraqi Sunni Arabs (at having lost power), the terrorist attacks were hurting more than government or coalition troops. There were still hiding places for terrorists, but fewer of them. And the growing police force and army put more Iraqi checkpoints and patrols in action.
Thus Saudi terrorist Abdullah Salih al Harbi was caught by Iraqi border guards, as he crossed over from Saudi Arabia. Al Harbi was on his way to Mosul, where he was to pick up weapons, and further instructions. Instead, al Harbi talked freely, providing names and addresses that led to more arrests in Saudi Arabia and Iraq.
There's one problem with the increased border security, it's hurting business for the smugglers. Consumer goods come into Iraq, and drugs (and other illegal goods) come into Saudi Arabia. For the border guards, the smugglers, who are often armed, are more dangerous than the terrorists. But you've got to stop them all and sort out who is who. The smugglers will offer a bribe you can afford to accept, but the terrorists have to be brought in.