The money to pay for the trigger was said to be wired from an Al Qaeda account by George Newbern, a stock broker. US stock brokerages (and foreign brokerages operating in the US) may not hold accounts that can be traced to known terrorist groups. In addition, McGee says that the money has been red flagged. Money itself cannot be red-flagged.
The frequency of the radio station WDRF is shown as 86.9 FM. However, the radio frequencies for commercial radios in the US range from 87.7 through 107.9 FM. This is common in TV and movies to use frequencies that are invalid to prevent representing a real radio station (similar to using 555 for phone numbers).
When Abby and DiNozzo and are reviewing information on their suspect on the computer, the headline on an online article reads "Woman Killed In Home Invastion Shooting".
The shooter at the beginning uses a Remington 7400 which holds 4 rounds but is fired 5 times without time for a reload. There could not have been a 5th already in the tube because he cocks before entering the booth.
When talking about the letter addressed to the station's PO Box, McGee says the letter had no postage and Ziva concludes it could only have been delivered by someone within the postal service. Since there was not postage, it would be impossible to determine the delivery method. Anyone could have placed the envelope on the subject's windshield or slid it under a door. The inference, however, is that it was retrieved from the P.O. box. That would mean that the person who placed it there had to either be a postal employee or someone who could enter the sorting room where access to the P.O. boxes is.