San Antonio FBI spokesman Rene Salinas, who is with the agency's joint terrorism task force, said it still isn't clear what the substance is. He said FBI testing conducted Sunday in Maryland came back negative for ricin, a deadly and easy to produce poison extracted from castor beans, and it is unlikely further testing will be done.
"There were no proteins in there to indicate it was in fact ricin," Salinas said.
A field test conducted by state authorities on the substance had come back earlier this week positive for ricin or a substance very close to it, Texas Department of State Health Services spokesman Doug McBride said.
Salinas, however, said the state's field test was "just a quick test and they don't check for the proteins in ricin."
The FBI spokesman said it isn't clear whether the FBI will continue with its investigation into how the mystery substance ended up in the roll of quarters. If it was put there as a joke, Salinas said "it was an extremely bad joke."
FBI agents from Maryland arrived in Texas on Saturday and retrieved the sample, which was then returned to Fort Detrick, a military base where the testing took place.
Roughly 400 residents of the Moore-Hill dormitory at the college were evacuated Friday night while hazardous materials crews cleaned and sanitized the dorm room and laundry room where the substance was found.
Students were back in their rooms by Saturday morning, and school officials said no students had shown symptoms of exposure, such as dizziness or respiratory problems.
Kelly Heinbaugh, a 19-year-old freshman, said the powder spilled onto her hands as she unwrapped a roll of quarters to do her laundry on Thursday. She said she'd used five other rolls of quarters her mother had gotten from the same bank and none had powder in them.
Heinbaugh and her roommate were both evaluated and cleared at a hospital.
People with ricin poisoning develop symptoms within a few hours of exposure.
University officials said this weekend they were confident all the students would be fine.