KANSAS CITY, Missouri (CNN) -- The man charged with shooting at motorists on Kansas City highways apparently fired a .380 pistol from his own car before speeding away, documents released on Friday said.

Authorities identified the suspect as Mohammed Pedro Whitaker. He is 27 and lives in Grandview, south of Kansas City, reported CNN affiliate KCTV-TV. He was charged with 18 felony counts covering nine incidents and is being held under $1 million cash bond.

Probable cause statements show police connected the shootings through .380 bullets found in the vehicles. Starting in early March, motorists told police of being shot at in the I-435/I-470/Highway 71 interchanges.

In several cases, the drivers reported seeing a dark green car near them driven by a man wearing sunglasses, a dark hoodie and sometimes a black ski mask.

One break came when a witness looking for a lost cell phone beside a road found a Walmart bag containing .380 ammunition, the documents showed. Prints on the ammunition boxes matched Whitaker's.

After police started shadowing Whitaker, he was observed trying to buy a .380 handgun with a laser sight from a man in a Bass Pro Shop parking lot, the statements said.

When police questioned the second man, he told officers he advertised the pistol online but refused to sell when Whitaker couldn't provide identification, the statement said.

Police served search warrants at Whitaker's residence on Monday and Thursday and found a .380 pistol, ammunition, sunglasses and three black hoodie sweatshirts, the statements show.

When questioned by police, Whitaker said he was one of the "highway shooter's" victims and claimed not to own a firearm, the probable cause statements say.

Jackson County, Missouri, prosecutor Jean Peters Baker, speaking at a press briefing, said Whitaker acted alone. She said he is being held on $1 million cash bond.

Baker wouldn't reveal much background on Whitaker but said he has "very little criminal record."

Whitaker is accused of shooting at nine vehicles, with two charges in each incident, Baker said.

Baker said surveillance, ballistics, more than 100 tips from citizens and witness statements helped authorities with their case.

"It wasn't built on one thing," she said. "It was built on a series of things."

Earlier, police said someone had fired a gun at as many as 20 motorists on major roads and highways. Baker didn't say if investigators suspected Whitaker in the other cases but that more charges may be filed.

Three people in vehicles were reported shot, none with life-threatening injuries. Whitaker was charged in two of those cases, Baker said.

Whitaker was arrested Thursday. Kevin Cooksey, who lives across an alley from the suspect, said he saw police take him into custody.

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"He couldn't go nowhere because he was surrounded. Completely surrounded," Cooksey told affiliate KSHB-TV. "They were on him. As soon as it happened, they were on him."

The shootings began March 8. Some motorists weren't even aware shots had been fired at their vehicles.

Jennie Baugher was driving along U.S. 71 when she heard something strike her car.

"I thought a big rock hit us," said the married mother of two from Roeland Park, Kansas. "My husband saw it the next day. Immediately when he told me that there was a hole in my car, I realized a bullet hit my car."

Mechanic found bullet holes

Tom McFarlin said he thinks shots at his vehicle came from a moving car on one of the ramps or overpasses.

"It was exactly where the highway splits," he said.

McFarlin was headed home to Lee's Summit, Missouri, on Interstate 470 south after watching his son's basketball game. Like Baugher, his car was shot in the evening, around 8:30.

When he took his car to mechanics a few days later, they discovered not one, but two bullets. The second one was lodged in the undercarriage.

Both cars were hit in the rear on the passenger side. The bullets lodged in metal and did not make it inside. In McFarlin's case, had the bullet made its way through the metal, anyone sitting in the passenger seat would have been hit.

Authorities had offered a $10,000 reward for information leading to an arrest in the case.

Fears calmed

Residents greeted news of the arrest with relief.

"It's actually been really nerve-racking," Marisol Sanchez told KCTV.

"It's really scary because I've been scared driving around," motorist Melissa Mitchell also told KCTV.

"Everybody is talking about the shooter, and now it's good that they have caught him in a short time," said gas station manager Bader Qureini.

Kansas City Mayor Sly James praised the investigators, saying, "Our citizens should have a heightened sense of security on the highways."

CNN's Dave Cera and George Howell reported from Kansas City, Missouri. CNN's Ed Payne and Ralph Ellis wrote this report in Atlanta.

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