On the al Hakim arrest

The arrest of al Hakim's son is a political ignition in the US Shia relationship in Iraq. The NYTimes has decent coverage.

But, I thought Juan Cole's take was far more interesting:

Al-Zaman says that al-Hakim's cell phone was confiscated, and hints broadly that the real reason for the arrest was to get access to his telephone records and the documents he had with him. The US suspects the Supreme Council for Islamic Revolution in Iraq of getting aid from the Iranian Revolutionary Guards, and Washington wants it stopped.....

....there was not good reason to doubt al-Hakim's passport, and it can't have taken 12 hours to call al-Maliki. There is also the question of why US troops were even in the area, since it is a Polish sphere of operations. They had to have come over for some specific purpose. The likelihood is that it was an intelligence operation of some sort.

We will probably never know the truth, but no one seems to believe this was an accident. So, what "greater purpose" was accomplished by straining the critical US-SCIRI relationship?

Was it intelligence? A warning to Iran? To SCIRI? To al-Hakim?