Flint Township Police Chief George said officers were at Dye Elementary School the day after the gun incident to talk with students, MLive.com reported.
"The student who owned the backpack, that student was interviewed by officers and is going to be interviewed again in the coming days," Sippert said.
Sippert said investigators had not yet determined if the gun came from the student's home or elsewhere, the news website said.
"We are still in the fact-finding mode," the chief said. "That's what we are trying to ascertain this morning. This will all be part of the investigation. I'm sure at some point we'll be talking to the prosecutor, bringing all the facts to the prosecutor. This may take a little time getting all the facts."
Genesee County Prosecutor David Leyton said if the weapon was taken from an unsecured location at home, there could be a fourth-degree child abuse charge brought against whoever was responsible, MLive.com said.
Carman-Ainsworth Superintendent Steven Tunnicliff said in a letter sent to parents that other students had alerted their teacher Monday morning when they realized a classmate had what appeared to be a gun.
Some parents said they were upset they were not notified immediately about the incident.
"I think Dye Elementary did a very poor job of informing parents on this matter," said one parent, Jennie Stein, who added "a letter is not acceptable in a situation like this."
The Flint Journal reported school officials notified police after confiscating the backpack and small-caliber gun, and determined there was no immediate danger to students and staff.
Tunnicliff said in the letter the student made "a significant mistake" by bringing the firearm to school, while adding school officials were satisfied "our other students followed what they have been taught and that the school protocols in place were followed."
Dye Elementary Principal Detra Fields and school counselor Aliza Grant met with the class after the incident to commend the students for paying attention to school safety, the Journal said.