A woman in Des Moines, Iowa, spotted an assault rifle on the roof of a police officer's squad car on Sunday afternoon.

"I thought maybe it was a bike rack at first or something, but I kind of seen it hanging over the edge and I was like no, I was like is that, I think that's like an assault rifle just sitting on top of their vehicle," Jones said.

Jones made a traffic stop of her own, waving down the officer at a red light.

"I approached him with caution and just told him and he was completely stunned," she said. "I could just tell on his face like he was a little confused and I keep telling him like, and I'm like pointing like, 'There's something up there that you might want to get,'" Jones said.

Des Moines Police Chief Michael McTaggart said in a statement posted to social media it was a "serious mistake," but noted the officer in the video is not at fault.

"At shift change, an officer was offloading his equipment, set his rifle on top of the car and then left, and left that rifle there. Next officer came in, checked that car out and didn't see the rifle on the roof and drove away," said Sgt. Paul Parizek. "I think we've all had a situation in our lives where we've misplaced something, we're looking for it, we walk by it two or three different times. That may help explain it. It definitely does not excuse what happened."

Jones said she's grateful she got the rifle off the roof before something happened.

"I said, 'What if it falls off?' [My niece said], 'Don't say that, we're behind him. Like, what if it, you know, fires off or something?'" she said.

Police said an internal review is underway.