Some 9/11 conspirators entered via Mexico?

That's what this says:

Some of the terrorists who helped with the September 11th attacks are now reported to have entered the country through Hidalgo County. State Representative Kino Flores, who sits on the state homeland security board, in an exclusive with Newschannel Five tells us these terrorists are said to have helped with the operation. Since then, the Valley's International Crossings have been under a tight watch with all incoming traffic being closely monitored.

As I parse this, he's referring not to those who were on the planes, but those who assisted them and weren't killed in the attacks. I wasn't able to find any additional information on this, but I sent him an email and will report back if I receive a reply.