Small bags inside a van whose driver was killed by an Immigration and Customs Enforcement agent contained salt, not drugs, said a lawyer for a witness, contradicting federal agents.

Investigators with the F.B.I. got a warrant to search the van on Tuesday after telling a federal judge they believed that a “crystal-like” substance in the plastic bags might be methamphetamine.

On Thursday, Ruby Powers, a lawyer for Victor Hugo Salgado Araujo, who is the victim’s younger brother and was a passenger in the van, said in a statement that “after consulting with my client and his family, our understanding is that this was granulated salt.”

Like other construction workers, her client and his brother would mix the salt into water and add lemon as a kind of homemade energy drink during their days working in the hot Houston sun, Ms. Powers said in an interview.

“He puts it in a water bottle and makes his own Gatorade, an electrolyte mix,” she added.

The Harris County district attorney, Sean Teare, also cast doubt on the presence of drugs Thursday. “Based on what we’ve learned about the passengers, it’s inconsistent that drugs were in the van,” he said in a statement.

The drug debate obscured, for the moment, the circumstances that led to the fatal shooting of the van’s driver, Lorenzo Salgado Araujo, by an ICE agent.