NEW UPDATE:

From the latest news:

The security officer killed in the gunbattle was 65-year-old Stan Cooper, a retired Las Vegas police officer who worked for a federal contractor providing security at the courthouse, according to a source.

The gunman opened fire about 8 a.m. inside the lobby of the Lloyd George U.S. Courthouse, 333 Las Vegas Blvd. South.

Las Vegas police spokeswoman Barbara Morgan said the shooter had been shot in the head.

“It looks like he went in there and just started unloading,” Morgan said.

The security officer was hit in the chest, and the deputy marshal was shot in the arm, he said. The 48-year-old marshal remained at University Medical Center in serious condition, though his injuries were not life-threatening, according to a source with knowledge of his injuries.

The gunman was shot and killed at the scene, FBI Special Agent Joseph Dickey confirmed. The gunman, who hid his gun under a black coat, died across the street, at the Historic Fifth Street School, 401 S. Fourth St., shortly after the shootout, he said.

Seven marshals and court security officers returned fire in the gunfight, Dickey said.

Investigators have not determined a motive for the shooting, but Dickey said "this was not a terrorist event."

Dickey also said the surviving court officer was in "good shape."

Authorities believe the shooter acted alone, Chief Deputy U.S. Marshal Roxanna Lea Irwin said.

The courthouse was evacuated and Las Vegas police cordoned off the area for several blocks.

After police arrived, paramedics wheeled at least two people out and down a ramp to ambulances. Dickey called the building evacuation “standard procedure” in such an incident, and said it was “for the safety of everybody in the place.”

"He walked into the courthouse and started shooting," U.S. Sen. John Ensign said.

Several downtown streets were shut down and traffic was diverted. Las Vegas Boulevard in the downtown area was closed to northbound and southbound traffic. The Las Vegas Academy, 315 S. 7th St., was on lockdown. The Regional Justice Center has been closed for the rest of the day.

Outside UMC a couple hours after the gunfire, a procession of more than a dozen police motorcycles and other vehicles escorted the body of Cooper from the hospital to the coroner's office.

About 20 law enforcement officers from the FBI, U.S. Marshals, Metropolitan Police Department and other agencies standing outside the UMC Trauma Center saluted as the procession drove by.

Jon McGovern, who runs a hot dog stand outside the Courthouse Bar & Grill, said he was setting up the stand around 8 a.m. when he heard two or three “pops” in quick succession, followed by other shots that “went in cycles.” He said at least 30 to 40 rounds were fired.

“It sounded like a fireworks show,” McGovern said.

He said that soon after the gunfire, about 30 to 40 people ran away from the shooting and down Lewis Avenue toward the restaurant shouting “Get down, get shelter.”

Mario Fenu, a defense attorney, said that about 8 a.m. he was walking on the sidewalk next to the courthouse heading toward the entrance when he heard a “pop.”

He said he thought it might be a gun but didn’t think it was near him because of the way sounds reverberate off the building, so he kept walking.

Five seconds later he heard “five pops” in succession, he said.

He said when he turned the corner he saw a man who didn’t appear to be a police officer in an “attack stance” aiming “a long gun” at the entrance of the building. The shooter was hiding behind a column.

Fenu said he saw another man behind a column on the far end of the patio, also in an “attack stance,” but couldn’t be sure if he was an accomplice, a law enforcement officer or an innocent bystander.

As Fenu ran away, he said the barrage intensified, possibly as marshals returned fire from the courthouse.

“I go to gun ranges and don’t hear that much ammo,” Fenu said.

Dozens of potential witnesses of the shooting were corralled inside the auditorium of the Las Vegas Academy where they were gradually being released about 10:45 a.m.

One attorney who declined to give his name said he stopped in the courthouse cafeteria before an 8:30 a.m. court appearance when he heard five or six shots.

"It was loud. It sounded like someone dropped a pan or something," the attorney said.

He said he didn't see anything but as he was later led out of the buidling, he saw bullet holes near the courthouse's front entrance.

He also said there might be more than 100 people in the school's auditorium.

U.S. Sens. Harry Reid and John Ensign have their Southern Nevada offices in the federal building. Neither was in the building this morning, aides said. Reid was at his home in Searchlight, a spokesman said.

Fifteen people work in Reid's office, while there are 10 who work for Ensign, according to aides in Washington. It was not known how many were in the building at the time, but whoever was there was evacuated along with other workers.

"All are physically OK," Reid spokesman Jon Summers said of the senator's staff.

“My thoughts are with the victims of today’s shooting and their families," Reid said in a statement. "The law enforcement personnel who protect the courthouse put their lives at risk every day to keep the people who are inside safe and I greatly appreciate their service.”

The Lloyd George U.S. Courthouse opened in 2000 and is named for a longtime senior federal judge who still hears cases.

 Photo courtesy of the R-J.