Virginia authorities are not sure what prompted a 20-year-old man to allegedly stab three people at random at a plasma donation center during a Fourth of July cookout.

Jairique Shannon entered the Octapharma Plasma in Petersburg, asked to used the restroom, and then began stabbing people with a long knife, Commonwealth's Attorney Cheryl Wilson told The Associated Press.

"There's no information that he had any grudge against anyone, and at this point we don't have a motive," Wilson said.

Shannon is charged with three counts of malicious wounding and is being held at the Riverside Regional Jail.

He'd donated plasma to the center at least once before, Wilson said. The center was holding a "customer appreciation cookout" to thank them for donating plasma at the time of the alleged attack.

Two females and a male were taken to a Petersburg hospital. The females were treated for unspecified injuries and released Thursday. The male was transferred to another hospital and was listed in critical condition.

Irene Banks told WWBT-TV that her daughter is the manager of the plasma center and helped stopped Shannon.

“He was telling me how she is a hero, said Banks of what she was told by police. "She took the man down, they said, my daughter did."

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In a Friday statement, the Charlotte, North Carolina-based plasma center said its "sole focus remains on supporting those involved and impacted in Thursday's event. We are working with authorities at this time to provide any help and information necessary."

Shannon also faces animal cruelty charges related to a police search of his Petersburg home. He is expected to appear in court Monday.

The Associated Press contributed to this report.