A spokesman for U.S. Immigration and Customs Enforcement says nearly half of those arrested during the largest immigration raid in a decade in the United States have been released.

In an email Thursday, Bryan Cox said more than 300 of the 680 people arrested Wednesday have been released from custody. He says about 30 were released at the plants and about 270 others were released from the military hangar where they had been brought after the raids to be processed.

He did not say why they were let go except to say those released at the plants had been let go due to “humanitarian factors.” Presumably that means that they were released because they had children in their houses. Wednesday’s raid came on the first day of school for those children.

He said those released “were placed into proceedings before the federal immigration courts and will have their day in court at a later date.”

Officials had said Wednesday that they would release detainees who met certain conditions, such as pregnant women or those who hadn’t faced immigration proceedings previously.

In a written release from the U.S. Department of Justice, officials said the releases were made on “humanitarian grounds.”

“All those detained yesterday were asked when they arrived at the processing center whether they had any children who were at school or childcare and needed to be picked up,” officials wrote in the release.

“In order to make it possible for detained aliens to contact family members and address childcare issues, HSI made cell phones available for use by detained aliens to make arrangements for the care of their children or other dependents. In addition, HSI (Homeland Security Investigations) had liaison officers working with the school districts to facilitate this process.

“As part of HSI procedures pursuant to this operation, if HSI encountered two alien parents with minor children at home, HSI released one of the parents on humanitarian grounds and returned that individual to the place from which they were arrested.”

“HSI similarly released any single alien parent with minor children a home on humanitarian grounds and physically returned that person to the place where he or she was originally detained. Based on these procedures, it is believed that all children were with at least one of their parents as of last night.”