Four Johnston teenage boys are suspected of sexually assaulting and robbing a 15-year-old boy earlier this month.

Morgan Andrew Hough, 18, Ritter Hayden Stahlbaum, 17, Kaden Allen Dishman, 15, and Noah James Lamar, 15, were arrested at Johnston High School on Thursday morning, police said.

They were each charged with second-degree sexual abuse, first-degree robbery and felony assault in connection with a Sept. 8 incident at Hough's home in the 8800 block of Highland Oaks Drive, Johnston Police Lt. Tyler Tompkins said at a Thursday morning news conference.

Tompkins declined to provide details about the allegations.

A Johnston police report said the victim suffered "apparent minor injury."

Hough and Stahlbaum were booked into the Polk County Jail, and they will be charged as adults, Tompkins said.

Lamar and Dishman were taken to Polk County Juvenile Detention Center, known as Meyer Hall.

Police learned of the attack on Sept. 18 after school officials received an anonymous tip, Tompkins said. Police investigated for several days, obtaining search warrants and interviewing students and parents, he said.

A video also was used as evidence in this case, court records show.

All four suspects and the victim are students in the Johnston school district. Tompkins said "they have interacted with each other in the past," but he wouldn't provide further details.

Three of the four suspects had been part of the Johnston wrestling program during at least part of the 2016-17 season, said Dragons wrestling coach Aaron Tecklenburg.

Dishman, now a sophomore, was on the team the entire season. Houg and Stahlbaum, now seniors, were removed from the 2016-17 team after the span of a few weeks, Tecklenburg said. Tecklenburg said he could not elaborate on the conditions for their dismissals.

Tecklenburg said he could not comment on whether Dishman would be on the team this season.

The case remains under investigation, Tompkins said. He declined to comment on whether there could be additional arrests, but he said: "We don't have any information that would point to anyone else that would be a target (for assault)."

Counselors have been made available for Johnston students who may need help coping with the situation, Tompkins said.

Laura Sprague, spokeswoman for Johnston Community School District, issued the following statement to media: "The district continues to work closely with the Johnston Police Department in full cooperation of their investigation. We will — and are — doing all we can to maintain a safe and orderly environment for all students and staff in our district."

She declined to provide further information, citing student privacy laws.

The assault is alleged to have occurred between 6 p.m. and 10 p.m. on Sept. 8, a Friday, at Hough's home. No one answered when a reporter knocked on the door of that home Thursday morning.

No firearms or other weapons are mentioned in the police report or court documents regarding this case.

Polk County Jail records show Hough was booked at 9:30 a.m. Thursday. A bond had not yet been set in his case as of Thursday morning.

Johnston police said Stahlbaum was also being held at the jail. A preliminary hearing in his case has been scheduled for Oct. 6, and bond was set at $60,000. A no-contact order issued Thursday prohibits Stahlbaum from going on school property and from being in the presence of anybody under age 18 without an adult present.

Criminal complaints in the case against Stahlbaum are not specific about how the five teens ended up at the Hough home or the nature of robbery.

Under Iowa law, prosecutors could seek to have Dishman and Lamar tried as adults, even though they are 15. Because the charges against Stahlbaum are forcible felonies, he will automatically be tried as an adult. Hough is an adult, although it was not immediately clear if he was 18 on the date of the alleged assault.

The Des Moines Register usually does not identify juveniles suspected in crimes unless they are being prosecuted as adults. The Johnston Police Department named all four suspects in a news release. State law changed in 2016 to keep more juvenile court records private, but an exception allows the public release of information about forcibe-felony allegations against children age 10 or older.