The guns used by a suspect in Monday's shooting on Interstate 17 involving law enforcement officers were firearms that were stolen from the Maricopa County Sheriff's Office several years ago, Sheriff Paul Penzone said Wednesday.

"On Tuesday morning I received a call advising me that the firearm that were used at the time of that shooting, as well as one additional firearm in the vehicle, both were firearms recovered that were stolen from the Maricopa County Sheriffs Office," Penzone said at a press conference.

The weapons went missing sometime between 2010 and 2015, Penzone said.

Three Arizona Department of Public Safety troopers were injured and a suspect was killed after the shooting on I-17 near Seventh Street, officials said.

The shooting occurred around 5 p.m. on the northbound side of I-17 just west of the Seventh Street exit, Phoenix police said. The incident shut down the freeway in both directions in the area until late the next morning.

The firearms used in the shooting went missing while former Sheriff Joe Arpaio was in office, Penzone said.

Arpaio admitted in 2014 that his department was missing nine firearms issued to the agency through a federal program that hands out surplus military gear to local law enforcement.

Arpaio said the agency picked up about 200 weapons from the surplus program shortly after he was elected in 1993, and 20 to 22 had vanished over the years. Some of those later were recovered.

"We're all responsible to ensure that we have great discipline when you're the head of an organization," Penzone said. "The lack of discipline that occurred in this organization from leadership and the impact that it's had on the men and women is unforgivable."

Penzone vowed he is taking steps to make sure another such incident never happens.

"As the sheriff I will do everything within my powers to ensure that this does not happen as long as it stays within our control," Penzone said.

He added: "I also committed to open the doors of this office to ensure that a thorough investigation is conducted relative to how this individual came into possession of those weapons."

In Monday's incident, Mesa police and DPS troopers began pursuing the man after he fled an incident that began in downtown Mesa.

Troopers stopped the driver, later identified as Arnaldo Caraveo, 27, in a white truck by ramming the truck's back end, forcing it to spin to a halt, said Sgt. Vince Lewis of the Phoenix Police Department, which is leading the investigation.

The man then exchanged gunfire with five Mesa police officers and three DPS troopers. Caraveo was shot and killed.

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