robberies targeting asians americans in philadelphia area

In Pennsylvania, state and local authorities suspect that they've uncovered a "shadowy organization" that has been terrorizing Asian Americans around Philadelphia and Delaware County with a series of gunpoint robberies and home invasions over the past two years: Cops warn Asian-Americans.

Last week, two men were charged with mugging a couple after they tailed their Mercedes-Benz from the mall back to their home. But there were three other similar cases in the same week involving Asian business owners, which prompted the District Attorney to put everyone on alert.

And this week, there were five more arrests, bringing the total number of arrests to seven: 5 More Arrests In Robberies Targeting Asian-Americans. The Philadelphia Police Department's Southwest Detectives, Pennsylvania State Police, the FBI and Delaware County were all involved in investigating the robberies.

The suspects can all apparently be linked to a larger crew responsible for dozens of armed robberies in the area, all targeting Asians. That's racist! My question is, according to the article, this "shadowy organization" has been targeting Asian Americans over the past two years. How is it that it took this long for authorities to figure out what was going on?