That means tighter security on rail lines everywhere. An alert to law enforcement officials in all 50 states has been sent out.
Mass transit has remained a target. It is the most vulnerable, according to Homeland Security officials and has been the focus of numerous terrorist plots in the U.S.
Could a 2007 sabotage incident targeting Metra be part of a terrorist plot? That's the question authorities are asking after information about a plot targeting trains was found in the paperwork or computer hard drives seized by Navy SEALs during the raid that killed bin Laden.
In 2007, several railroad spikes were removed from the tracks used by Metra's Electric and South Shore lines. Despite a $50,000 reward, the FBI has not found those responsible.
"It is still an active case. Fortunately, we haven't had any other circumstances like this since then, and we will continue to be very vigilant in surveying all of our property," said Judy Pardonnet, Metra spokesperson.
Congressman Bobby Rush rode a Metra train Friday, saying Chicago needs to stay vigilant.
"We knew that in the mind of that madman, Chicago was present in his mind. Praise be to God, he was never able to fulfill his desire and execute his plans," said Rush.
Congressman Rush and other officials joined with Metra leaders Friday morning to officially dedicate the new 35th Street train station on the Rock Island line. The new station offers a mass transit alternative for White Sox fans going to U.S. Cellular Field.
Metra has stepped up security at some of its train stops in the wake of the warning from Homeland Security. Materials indicated that al-Qaida was interested in targeting Chicago, New York, L.A. and Washington.
"You can't guard hundreds of miles of track, and if they can get to one location that is not well guarded and put explosives on it or do something to cause the train to derail, that is a lot easier than going after an aircraft," said Richard Clarke, ABC News consultant.
Homeland Security issued a bulletin saying that as of February 2010, al-Qaida was allegedly contemplating conducting an operation against trains at an unspecified location in the United States on the tenth anniversary of September 11, 2001. As one option, al-Qaida was hooking into tipping a train by tampering with the rails so that the train would fall off the tracks at either a valley or a bridge.
The CTA is now on a heightened state of vigilance, and Amtrak said it will employ appropriate countermeasures when necessary.
One U.S. official who spoke on the condition of anonymity says the plot was aspirational. He says it was just a plan, nothing had been set in motion.
