A passerby shot and killed a suspect who was attacking a Lee County Sheriff's Deputy in Florida, according to witnesses on the scene.

Officials with the Lee County Sheriff's Office and Florida Highway Patrol blocked off exit 123 on I-75 Southbound in Estero for about 12 hours Monday to investigate the fatal shooting, which began with a high-speed chase.

"[He was] going at least 120 mph," said Nicole Ambrosimi. "There was like a trail of dust behind him because he was going so fast and I felt, like, that kind of wind jolt as he passed by," she added.

Ambrosimi was traveling in the far left lane on I-75 South and says the suspect was traveling in the left shoulder of the highway, by-passing traffic.

Deputy Dean Bardes was responding to an unrelated accident when he noticed the suspect speeding and began to pursue him.

Ambrosimi's daughter said when the suspect stopped, he left his vehicle and began to attack Deputy Bardes.  "He just came up out of nowhere and attacked a deputy, said Alyssa Rivera, Ambrosimi's daughter.

"He got on top of him and started punching him and just being really rough and wrestling with him," said Rivera.

She believes the attack went out for about 3 minutes before a passerby stepped in. They said they did not see the shooting, but the mother and daughter heard from others in traffic who were in viewing range of the incident.

"From what I heard from reports the deputy had instructed the Samaritan to shoot the suspect," said Ambrosimi.

Very few details have been released from the sheriff's office at this stage of the investigation.

"We don't have a lot of information; it's very fresh right now," said Lt. Jeff Detkas, during a morning press conference.

A follow-up presser scheduled for Monday afternoon was abruptly canceled.

"It was unfortunate that a life was taken today but I am very grateful to the good Samaritan and the timely work of the deputy," said Ambrosimi.