(CNN) -- An alleged sexual assault of a Texas girl involving nearly 20 people was recorded on cell phones, and a video of the alleged incident was circulating among students in her school district, according to court documents obtained Tuesday.

As of Monday, 13 adults and five juveniles had been arrested as part of the investigation, authorities said. A defense attorney for one of the suspects told CNN affiliate KPRC that the number of suspects could increase.

"I don't know the exact number of people involved," James Evans said. "I've heard as many as 28 or more."

The case has sharply divided the community, according to CNN affiliate KHOU, which reported the girl was 11 years old.

Darrel Broussard, assistant police chief for the Cleveland, Texas, Police Department, said Monday that the investigation into the incident "is continuous," with more significant developments possible. Cleveland is about 50 miles northeast of Houston.

"There have been leads during our investigation that have alerted us to other possible persons of interest," Broussard told CNN. "The investigation is ongoing."

The 18 individuals charged thus far are between 14 and 27 years old, he said. Those who are adults were indicted last month on a charge of aggravated sexual assault of a child.

On Friday, the Cleveland Police Department announced that four students in the Cleveland Independent School District had been arrested on charges of aggravated sexual assault of a child under 14. The juveniles appeared Monday in a Liberty County court in the town of Liberty.

Police noted that some but not all suspects are students at Cleveland High School.

Mike Little, the district attorney in Liberty County, said police would likely decide whether more people would be charged. He offered few other details, saying Monday, "We are very careful about pretrial publicity."

The incident allegedly happened November 28 at two residences in Cleveland, according to a search warrant affidavit obtained by CNN on Tuesday.

The girl told a school district police chief about the incident, who notified Cleveland police on December 3, the affidavit said. The chief then interviewed employees of the Cleveland Independent School District who had heard of the incident, according to the documents. One employee spoke with several students "who had seen the cell phone videos or heard of the incident," according to the affidavit.

The girl told a forensic interviewer from a child advocacy center that one suspect called her "and asked if she wanted to ride around" on that day, the affidavit said. Three of the suspects picked her up and took her to one residence where a fourth suspect lived. The fourth suspect told her to take her clothes off, she said, adding that "he would have some girls 'beat her up' or she would not be taken back to her residence if she did not comply." the affidavit said.

The girl said she engaged in sexual acts in the bedroom and bathroom of the residence. While in the bathroom, she said, she heard one suspect on the phone inviting other people over to have sex with her, and said when she came out of the bathroom four men she did not know were there, the affidavit said.

The aunt of the suspect arrived home, however, and "the victim and the other individuals left the residence in haste through the rear window of the house," according to the affidavit. After leaving, the girl said she and the others went to an abandoned trailer where the sexual acts continued, the affidavit said.

"Victim stated that digital still images and digital video images of the sex acts were recorded by one or more individuals using cellular telephones," according to the affidavit.

Broussard told CNN on Tuesday that it took authorities months to investigate the incident and obtain indictments and arrest warrants. "To put together the case, it takes time to do that," he said.

CNN's Ashley Hayes contributed to this report.