Agents from the Federal Bureau of Investigation, Texas Department of Public Safety, Department of Homeland Security, and Bureau of Alcohol, Tobacco, Firearms and Explosives responded to the shooting, he added.

The gunman’s motive is still unknown, Sheriff Meeks said.

Of those injured, 12 were wounded by gunfire. Information was unavailable on how the two others were injured. At an earlier news conference, officials said they believed the gunman had used a semiautomatic rifle, but they later said they believed it had been a handgun.

The shooting took place at the Party Venue, a family-owned party hall near Greenville, about 50 miles northeast of Dallas, at a Texas A&M University-Commerce homecoming party that had not been sanctioned by the school, officials said.

In a statement posted on Facebook on Sunday, the university president, Mark Rudin, said the shooting “has touched and saddened our university community.”

“There is a tremendous amount of misinformation revolving around this off-campus event,” the statement continued. “At this time, we can confirm four of our current students were treated and released from local hospitals. We are currently reaching out to these four affected students. We will continue to monitor this situation.”

Donna Jackson, who owns and runs the Party Venue with her son, said the group from the university that had rented the space had done so for parties at least twice in the past without any problems. She could not recall the name of the group.

Those who contract to use the venue must provide security, she said.

Ms. Jackson learned about the shooting after a cousin texted her. Videos of the carnage posted to social media have “shaken me to my core, to see the chaos going on in there,” she said.