That certification is a key step in qualifying them for a special visa they would not have otherwise been eligible for.Texas’ Bexar County Sheriff Javier Salazar expeditiously signed certification forms for all of the migrants, according to Boston-based immigration attorney Rachel Self, who went down to San Antonio to obtain the paperwork."Based upon the claims of migrants being transported from Bexar County under false pretenses, we are investigating this case as possible Unlawful Restraint," Salazarsaid in a statement to GBH News."We have submitted documentation through the federal system to ensure the migrants’ availability as witnesses during the investigation."Related Stories- Feds probe how DeSantis paid for migrant flights to Martha's Vineyard- Basic Black: What happens when human lives are used as political pawns- 'This has changed me': Vineyarders say migrants transformed their lives, missions- Attorneys lay out legal options for Martha's Vineyard migrants, including a visa for crime victimsMany of the migrants told media they’ve come to the United States to seek asylum, and were sheltering at the Migrant Resource Center in San Antonio when they were approached by a woman who identified herself as “Perla.” They were falsely promised jobs, housing and education."