(CNN) -- A Prince George's County, Maryland, police officer has been suspended, and prosecutors are investigating an incident -- caught on video -- in which officers wielding nightsticks beat a University of Maryland student, officials said Tuesday.

Authorities also are looking into documents filed by police in the case that appear to contradict the video, Prince George's County police Lt. Andy Ellis said.

The video was shot March 3 after the Maryland men's basketball team defeated Duke. In the video, students can be seen celebrating the win as officers in riot gear and on horseback are nearby. Some students are holding up their cellphones, taking pictures or video of the officers and the celebration.

The video shows a student identified as John "Jack" McKenna skipping down the street and approaching two officers on horseback. After a brief exchange, two officers on foot slam McKenna against a wall and he falls to the ground. A third officer joins the first two, and the three strike McKenna with nightsticks while he is on the ground as other students scatter.

McKenna had a cut on his head that required eight staples to close, said Sharon Weidenfeld, a private investigator working for McKenna's attorney, Chris Griffiths. In addition, he had a concussion, a badly swollen arm and bruises elsewhere on his body. Griffiths' office referred questions to Weidenfeld on Tuesday.

Another man identified as Benjamin Donat was also beaten, although that incident was not shown on the video, Weidenfeld said. On Donat's body, the imprint of the officers' nightsticks could be seen, she said. He also suffered a head injury that caused him some memory loss for a few days, although he will be all right, Weidenfeld said. "He really had his bell rung," she said.

Weidenfeld discovered the video and would say only that it was shot by another University of Maryland student.

Authorities arrested Donat and McKenna on suspicion of assaulting an officer and disorderly conduct. Documents filed by police allege that the two were causing a disturbance and that they struck mounted officers and their horses, causing minor injuries, when authorities intervened.

"Arrested 1 and Arrested 2 were both kicked by the horses and sustained minor injuries," the charging documents said.

The video does not show McKenna striking the mounted officer or horse, and the horses were not nearby while the beating was taking place. The documents tell a "totally fabricated story," Weidenfeld said Tuesday.

Prosecutors dropped charges against Donat on Friday and McKenna on Monday, she said. Griffiths is representing both youths, and a lawsuit is planned against the officers, Weidenfeld said.

"I was very disappointed to see the conduct of my officers on the tape," Prince George's County Police Chief Roberto Hylton said at an afternoon news conference. "I'm very disappointed in what I saw."

He emphasized that he wanted to make sure that the officers, once identified, get a "fair and impartial investigation." Although he came down on the officers seen on the tape, he also said the students' celebration involved setting fires, rocking buses and throwing things at officers.

"There is a two-party fault here: the students, but also you can see I am very disappointed by the actions of my officers," he said.

The department's internal affairs unit is investigating the incident, and will assist Prince George's County prosecutors in their probe, Ellis said.

"The charging documents certainly do not appear to be supported by the video," Ellis said. But he said, "I'm sure it's a stretch to say it's a cover-up," saying it's likely the officer who wrote the documents had a "miscommunication" with officers involved in the incident, who provided information.

Read the charging documents from CNN affiliate WJLA-TV (PDF)

The department's internal affairs unit is investigating and will assist Prince George's County prosecutors in their probe, he said.

Ellis said he did not know whether the officer suspended wrote the charging documents. Because the officers on the video were in full riot gear, they could not be readily identified, but authorities are looking into who was on duty that night and where officers were at the time to determine who was involved.

"We didn't know about this videotape until it came out yesterday morning," he said. "We had no idea. It's kind of caught us by surprise. As evidence comes out, or we learn more information, we'll suspend officers as they become identified."

He added, "Not only is the conduct of the officers on tape excessive -- and clearly it's excessive -- there are other issues here we need to work through to make sure we're more organized" in such situations.

The officers on horseback were from the Maryland-National Capital Park Police. Department spokesman Lt. Stanley Johnson said the mounted officers were there for crowd control purposes. While "there were a lot of activities" going on that night, he said, no department horses or officers were injured and there were no reports of people being kicked by horses.

In a statement Monday, McKenna's family told CNN affiliate WJLA-TV in Washington that "some of these characters ought to go to jail. ... Some ought to merely be booted off the force, and the remainder should be properly trained to discover that force is not always necessary, and brutality is always wrong."

The U.S. Justice Department is aware of the video and is "looking into it," Weidenfeld said Tuesday.

She said she is surprised officers would take such action knowing that so many people were filming the celebration.

Prince George's County police arrested 28 people after the basketball game, WJLA reported. Of those, 23 were students.

The police department emerged from federal oversight about 14 months ago, according to the station. The Justice Department had monitored it after complaints about officers using unnecessary force.