The bombs are built and placed by one of several dozen independent gangs, each containing smaller groups of people with different skills. At the head of each gang is a guy called the money man. That tells you something about how all this works. Nearly all the people involved with IED gangs are Sunni Arabs, and most of them once worked for Saddam. The gangs hire themselves out to terrorist groups (usually al Qaeda affiliated), as well as Baath Party or Sunni Arab groups that believe the Sunni Arabs should be running the country. You got the money, these gangs got the bombs.
The money man, naturally, calls the shots. He hires, individually or as groups, the other specialists. These include scouts (who find the most effective locations to put the bombs), the bomb makers, the emplacers (who place the bomb) and the trigger team, that actually sets the bomb off, and often includes an ambush team, to attack the damaged vehicles with AK-47s and RPGs. The trigger team also usually includes a guy with a video camera, who records the operation. Attacks that fail, are also recorded, for later examination for things that could be improved.
The specialists most in demand are the emplacers. This is the most dangerous job, as coalition and Iraqi troops watch carefully for IEDs being placed, and shoot fast, and to kill, if they see a bomb being planted. Needless to say, the highest casualties are among the emplacers.
Many of these specialist teams are independents, and hire themselves out to the money man who pays the best, or has a reputation for not losing people. Some of these teams have been found advertising on the Internet. Men in each team get from $50 to several hundred bucks for each IED worked on.
Interrogations of captured IED crew members indicates that most IED teams operate on a two week cycle. During this period, the gang will prepare and place from a few, to a dozen IEDs in one, carefully planned operation. Once the money man has decided on what area to attack, the scout team (or teams) spend 4-5 days examining the target area, to see how troops, police and traffic operate. They recommend places to put the bombs, and the money man decides how many to build and place where.
The bomb makers are contracted to build a certain number of bombs and have them ready for pick up by the emplacers on a certain day. The trigger teams are either already in place, or arrive shortly after, the emplacers successfully plant their bombs. Most of the bombs are discovered and destroyed by the police or troops. Increasingly, the trigger teams are discovered, and attacked, as well. This is where a lot of bomb team members are captured. These men often provide information on other members of the team, which results in more arrests. Thousands of men, involved with these IED gangs, have been killed or captured in the last two years. There are always plenty of new people willing to have a go at it. The main reason is money. With over 20 percent unemployment nationwide, and even higher rates in Sunni Arab areas (because the terrorism there has reduced economic activity), an opportunity to make a months pay for a few hours, or days, work, is worth the risk. For the more senior members of the gangs, there is another reason. These guys worked for Saddam, have blood on their hands, and are known to the Kurds and Shia Arabs they terrorized for years. They can either flee Iraq, and risk getting picked up eventually for their crimes, or stay in Iraq, and hope that their IED efforts put Sunni Arabs back into power before the police, or vengeful kin of their victims, catch up with them.
Saddams henchmen got away with hundreds of millions of dollars in cash. We know this, because that much was seized by coalition troops as they overran Iraq in 2003. The current IED campaign is costing the terrorists one or two million dollars a month. Nearly a hundred IED and car bomb factories have been captured so far, and often large quantities of cash are seized. The IED campaign is driven by the cash, all the bombs, explosives and shells Saddam had stored all over the country, and Sunni Arab fear of being brought to justice.
A small percentage (less than 20 percent) of the terrorist attacks are by al Qaeda, which has a different agenda than the Sunni Arabs. These differences (al Qaeda wants an Islamic dictatorship, Saddams buddies want a Sunni Arab secular dictatorship) have been put aside, as both groups try to get the foreign troops out of Iraq.
Al Qaeda prefers to use car bombs. This is because al Qaeda has a big supply of Sunni Arab volunteers from neighboring countries. Many of these volunteers are worthless, as they have no training, and some of them are deranged. But some of these men are capable of driving a suicide car bomb, used as trigger teams. The car bombs are produced in auto repair shops, where cars have seats, and other components removed so that the explosives can be installed. Better suspensions are often installed so that the vehicle will not be so obviously overloaded, and be easier to drive. Building a car bomb costs more than an IED, but al Qaeda saves money by using volunteers for other jobs, besides drivers. The emplacers will drive another car, behind the suicide bomber, radioing the suicide bomber instructions, and sometimes setting off the explosives themselves. Suicide bombers often have second thoughts when it comes to doing the deed. The emplacers prevent this any way they can. The emplacer car will often have a cameraman, taping the operation. These vids turn up a lot on pro-terrorist web sites.
There is no terrorist high command for the IED effort. All of the gangs are independent, and many of the teams within the gangs are independent as well. What drives the operation is money, a desire to regain control of the country, and fear of punishment for past crimes. The ongoing political negotiations between the Shia Arab, Sunni Arab and Kurd leaders, has dealt with the subject of amnesty for Saddams most notorious thugs. The victims (or their surviving kin) are reluctant to let the current bunch of terrorists off scot free, but are willing to negotiate over the issue. The more blood people have shed, the harder it is to get an amnesty deal. The terrorists currently in the game are taking a big gamble, that they will either see Sunni Arabs back in power, or that they will evade punishment once the police gain control over the entire country.
There are currently some 30-50 IED (roadside, or suicide car bomb) attacks attempted each day in Iraq. These bombs kill 20-30 American troops a month. They are the most effective weapon the Sunni Arab and al Qaeda terrorists have, even though the vast majority of the bombs are detected and destroyed before they can be detonated.