What to know about the investigation of the Perry High School shootings

The investigation of the Perry High School shootings that left the gunman and a sixth grader dead and the principal in critical condition now turns to the question of why and how the tragedy happened.

Here is what we know about the probe.

What are the next steps in the investigation of the Perry, Iowa school shooting?

The Iowa Division of Criminal Investigation is leading the investigation, as is typical in complex homicide cases.

Mitch Mortvedt, a DCI assistant director, did not respond to requests for comment Friday. In a news release, the Iowa Department of Public Safety said detectives were still interviewing witnesses and reviewing witness accounts. Investigators also seized "large volumes" of digital and social media evidence, according to the release.

The electronic evidence "will take time to review," the news release said. Once the Iowa DCI finishes its investigation, a report compiled by DCI investigators will be turned over to the Dallas County Attorney's Office to determine what steps, if any, to take next, it said.

What do we know about Dylan Butler, who opened fire at Perry High School on Thursday?

The gunman, Dylan Butler, 17, was a Perry High School student. Armed with a pump-action shotgun and a small-caliber handgun, he apparently hid out in a bathroom before opening fire in the school at 7:37 a.m. Thursday while students at the high school and adjacent middle school were eating breakfast, according to authorities.

He shot eight people — five students, Principal Dan Marburger and two other staff members ― according to authorities. On Friday afternoon, they identified the Perry Middle School sixth-grader who died as Ahmir Jolliff, 11.

Butler was the son of Jack Butler, the manager of Perry Municipal Airport and former public works director for the city. An autopsy confirmed Dylan Butler died of a self-inflicted gunshot wound, Friday's news release said.

Butler made numerous posts on social media before the shooting, including a TikTok selfie Thursday morning of him in a school bathroom with a blue duffel bag by his feet and a caption reading "Now we wait." DCI investigators are looking into the posts as part of the investigation, Mortvedt said Thursday.

A law enforcement official briefed on the investigation told the Associated Press that federal and state investigators were interviewing Butler’s friends and analyzing his social media profiles. Investigators also have found other photos Butler posted of himself posing with firearms, according to the official, who was not authorized to publicly discuss details of the investigation and spoke to Associated Press on condition of anonymity.

Sisters Yesenia Roeder Hall and Khamya Hall, both 17, told the Associated Press Thursday that Butler was their friend and would come over to their house to watch movies and eat with them. Butler had been bullied relentlessly since elementary school, but the situation escalated recently when his younger sister started getting picked on, too, they said. His parents brought up the issue to the school and that was the “last straw” for Butler, they said.

“He was hurting. He got tired. He got tired of the bullying. He got tired of the harassment,” said Yesenia Roeder Hall, 17. “Was it a smart idea to shoot up the school? No. God, no.”

Dylan Butler also responsible for improvised explosive device at Perry High School, fire marshal's office said

In addition to the shootings, Butler was responsible for an improvised explosive device police officers found as they searched the school Thursday, Ron Humphrey, a special agent with the Iowa State Fire Marshal's Office, confirmed Friday.

Agents from the Iowa State Fire Marshal's Office and federal Bureau of Alcohol, Tobacco, Firearms and Explosives, disassembled the device Thursday, Humphrey said.

It was "rudimentary," Humphrey said, adding that he was not sure how much damage it might have done had it gone off.

"It's hard to say with these things," Humphrey said. "I don't like to speculate."

'If you see something, say something:' Police urge everyone to be vigilant of social media posts following Iowa school shooting

West Des Moines police on Friday reported they had arrested a man who made social media posts supporting Butler and making threats against local schools. Echoing the police in their news release, Iowa State Patrol spokesman Sgt. Alex Dinkla urged anyone who sees disturbing social media posts to call 911.

"Report it. Let authorities know. If you see something, say something," Dinkla said. "That's always a good lesson I think everybody should always go by. You never know when it might affect or change somebody's life or save somebody's life."

Philip Joens covers public safety, retail, real estate and RAGBRAI for the Des Moines Register. He can be reached at 515-284-8184, pjoens@registermedia.com or on Twitter @Philip_Joens.

This article originally appeared on Des Moines Register: What's next in investigation of Iowa school shooting, gunman Dylan Butler