This is a highly opinionated discussion of Able/Danger. However, it has some additional information about the sort of data mining that was going on:

According to military sources familiar with the Able Danger legal
side, the effort stepped over the line when LIWA contractors purchased
photographic collections of people entering and exiting mosques in the United
States and overseas. One source says that LIWA contractors dealt with a questionable source of photographs in California, either a white supremacy group or some other anti-Islamic organization.

"There are records of who goes where regarding visits to mosques," Shaffer told Government Security News. "That was the data that LIWA was buying off the
Internet from information brokers." It was stuff no one else bothered to
look at, says Shaffer.

LIWA purchased an open-source, six-month data run, Shaffer
says, and analysts developed a set of eight data points common to 1993 World
Trade Center bombers and associates. With advanced software, including facial recognition software able to track individuals from the collected photographs, Shaffer says contractors "made the link between [Mohammed] Atta and [Sheik Omar Abdel] Rahman, the first World Trade Center bomber."

It also includes a link to a reminder, from the Pentagon, about why the Pentagon has rules preventing the Pentagon from collecting information on US persons, (because intelligence agencies where used for political purposes only 3 decades ago), and exactly what those rules are.

The real story here is how another renegade intelligence effort subsisting on hyper secrecy ran afoul of regulations first implemented in the Ford administration when U.S. intelligence agencies were caught collecting information on community, religious and labor leaders, civil rights protestors, and anti-Vietnam war demonstrators... 

"What began as a force protection mission for DOD organizations, evolved, through mission creep, lack of clear rules, and the lack of meaningful oversight, into an abuse of … Constitutional rights…," William Dugan, Pentagon chief of intelligence oversight, said last week. He was describing the experiences of the 1960s and 1970s.