Originally Published: 12 APR 23 02:59 ET

Updated: 12 APR 23 11:07 ET

By Aya Elamroussi, CNN

(CNN) -- As officials in Louisville, Kentucky, prepare to host a vigil to grieve the five people killed Monday in a downtown bank shooting, the 25-year-old gunman's family released a statement saying he struggled with depression but they had no idea he was plotting the attack.

"While Connor, like many of his contemporaries, had mental health challenges which we, as a family, were actively addressing, there were never any warning signs or indications he was capable of this shocking act," Connor Sturgeon's family said in a statement to CNN affiliate WDRB.

The family said it has many "unanswered questions" and is cooperating with the investigation.

"No words can express our sorrow, anguish, and horror at the unthinkable harm our son Connor inflicted on innocent people, their families, and the entire Louisville community," the statement read.

"We mourn their loss and that of our son, Connor. We pray for everyone traumatized by his senseless acts of violence and are deeply grateful for the bravery and heroism of the Louisville Metropolitan Police Department."

Officials Wednesday also are expected to release audio of 911 calls about the shooting, Louisville Mayor Craig Greenberg told CNN's Wolf Blitzer on Tuesday evening. The attack was just one of more than 145 shootings reported in the US this year with at least four people shot, excluding the shooter.

Police on Tuesday released dramatic police body camera footage of parts of the shooting at Old National Bank, in which authorities say the bank employee opened fire on his colleagues and then engaged in a shootout with police before he was shot dead.

The attacker, livestreaming the gruesome assault, fatally shot five of his coworkers in Kentucky's most populous city around 8:30 a.m., about 30 minutes before the bank was to open, authorities said. Several others were hospitalized, including a rookie police officer who was shot in the head and was in critical condition Tuesday.

"Our city is heartbroken," Louisville Mayor Craig Greenberg told CNN's Wolf Blitzer on Tuesday evening. "These five victims should not be dead -- just like everyone else who was killed by gun violence in our city, in our country, should not be dead."

It's still not clear what provoked the shooter to go on the deadly rampage. Sturgeon used an AR-15-style rifle -- the choice weapon of many US mass shooters -- he'd legally bought six days before the attack, police have said.

Kentucky has some of the least restrictive gun laws in the US: no "Red flag" laws, no universal background checks, permitless concealed carry and no waiting period between buying a firearm and taking possession of it. Those relaxed gun laws, experts say, help explain why the state has a firearm death rate higher than the national average, according to the CDC.

The city will hold a vigil at 5 p.m. Wednesday at the Muhammad Ali Center in Louisville, the mayor said.

The vigil will "acknowledge the wounds, physical and emotional, that gun violence leaves behind," Greenberg told reporters Tuesday. "It will be an interfaith opportunity for our entire community to come together -- to grieve, to heal, to begin to move forward."

What the body camera footage shows

On Tuesday, Louisville police released bodycam video and bystander footage showing the officers' response to the mass shooting.

The public footage begins with a video from Officer Nickolas Wilt -- a 26-year-old who'd graduated from a police academy just 10 days prior -- who drove up to the scene with his training officer, Cory "CJ" Galloway.

As Wilt ran toward the gunshots that officers faced upon arrival, he was shot in the head, police said. The released version of Wilt's footage cuts off before he is shot.

Galloway's body camera footage shows him taking fire and then scrambling down some stairs to a safe position behind a planter. He tells other officers he can't see the gunman but notes the gunman is shooting through windows in the front of the bank, the video shows. At some point, Galloway was also shot.

The gunfire shattered the bank's lobby glass windows, giving officers a view of his location, Deputy Chief Paul Humphrey said.

As other officers arrived on scene, Galloway shot and killed the gunman from the steps in front of the bank, the video shows.

"I think I got him down! I think he's down!" Galloway said, the video shows. He then advanced toward the building and directed others to check on his fallen colleague. "Suspect down. Get the officer!"

The bystander footage, also released by police, was filmed across the street from the bank. The video shows Galloway taking cover behind the planter with his gun raised and pointed toward the building as he tries to locate the gunman's position.

The entire situation -- from when the gunman began firing his assault weapon to when he was killed by police -- lasted for about nine minutes, according to Louisville police Lt. Col. Aaron Cromwell.

Those killed in the shooting were Joshua Barrick, 40; Juliana Farmer, 45; Deana Eckert, 57; Tommy Elliott, 63; and James Tutt, 64, police said.

Nine people -- including Eckert, before she died Monday -- were hospitalized after the shooting, officials said. Among the eight current survivors, five had been discharged as of Tuesday, a hospital spokesperson said.

The three victims who remained hospitalized Tuesday include Wilt, who underwent brain surgery and was in critical condition, and two others who were in fair condition, the hospital spokesperson said.

Shooting happened in one minute, official says

It took the assailant one minute to complete the bloodbath before he stopped and waited for police to arrive, according to footage of the massacre described by a city official to CNN.

The shooter had livestreamed the gruesome attack on Instagram. The video has since been taken down.

The Instagram video begins by showing an AR-15-style weapon, followed by a worker in the bank saying good morning to the gunman, the official said.

The gunman then tried to shoot her in the back but failed because the safety was on and the weapon still needed to be loaded, the official said. Once the shooter loaded the weapon properly and took the safety off, he shot the worker in the back, the official said.

The assailant then continued his rampage, firing at workers while they tried to outrun him, the official said. The shooter did not go to other populated floors of the bank, the official said.

Once the shooter finished firing, he sat in the lobby area that looks out onto the street, apparently waiting for police, the official said. Police arrived about a minute and half later, the official said.

Staff members were holding their morning meeting in a conference room when the gunman opened fire, bank manager Rebecca Buchheit-Sims told CNN.

She said the massacre "happened very quickly." Buchheit-Sims attended the staff meeting virtually and watched in horror as gunfire exploded on her computer screen.

"I witnessed people being murdered," she told CNN. "I don't know how else to say that."

Sturgeon had interned at the bank for three summers and been employed there full-time for about two years, his LinkedIn profile showed.

The assailant had been notified that he would be fired from the bank, a law enforcement source said Monday. However, the mayor said he doesn't believe the shooter was given a notice of termination. "From what I have been told from an official at the bank, that is not accurate," Greenberg told reporters Tuesday.

A former high school classmate of Sturgeon's who knew him and his family well said he never saw any "sort of red flag or signal that this could ever happen."

"This is a total shock. He was a really good kid who came from a really good family," said the classmate, who asked not to be identified and has not spoken with Sturgeon in recent years. "I can't even say how much this doesn't make sense. I can't believe it."