It seems the Fair Oaks people tried to do everything right & still was hoodwinked by an "illegal", who was one of the participants in the recent animal abuse video. 

The following is copy/paste from FJ AgWeb. Please read it in entirety:

Following the release of the first activist video shot at Fair Oaks Farms, the local sheriff’s department issued warrants for the four individuals involved. One of those employees, Edgar Gardozo-Vasquez, 36, was arrested this week and according to ICE officials was working in the country illegally – a startling reminder than the e-verify system is broken. Gardozo-Vasquez, who is from Mexico, was arrested by the U.S. Border Patrol in 2005. Fair Oaks Farms is listed in the E-Verify database as a participating employer. And according to a the IndyStar, the farm worked with a law firm to ensure proper documentation. 

“Every employee is required to and provides a Social Security number and all appropriate legal documentation for employment to our company," Fair Oaks said in a statement to IndyStar. "We work with one of the U.S.’s leading farm labor law firms, Davis & Goldfarb, to provide that documentation to the federal government.”

So you if Fair Oaks ran his paperwork through e-verify, then the system would have alerted him to his previous arrest and deportation. Except, that’s not always how it works. 

According to Kevin Paul, attorney and owner of Range Law e-verify is not fail safe. He says the system often says an employee isn’t eligible to work who is eligible and vice versa.

“We suggest that farmers be very careful about enrolling in e-verify,” he says. “Right now, we don’t have to do this under the law in most states.”

For years various e-verify loopholes have been exposed including it’s inability to detect misrepresented identity. 

The system does not have photo matches for state-issued identification, Kelly Fortier, partner and immigration sub-practice leader with Michael Best & Friedrich, LLP.

The e-verify system processes employee I-9 form information through two separate databases, the Social Security Administration's database and the Department of Homeland Security databases, according to Fortier. 

“There’s a good chance e-verify would not have flagged someone using someone else's state ID card and a social security number,” Forteir says. She says the system is more likely to catch the misuse of documents issued by the federal government, for example, through the permanent residence card, which is issued by the Department of Homeland Security.