The gunman who killed four people at an office building in New York City on Monday evening left his home in Las Vegas, Nevada late last week, traveling across the country to execute a mass shooting inside the building that houses the NFL headquarters in Midtown Manhattan.

Based on a note 27-year-old Shane Tamura left before killing himself, New York City Mayor Eric Adams said he seemed to be targeting the NFL, though he never made it to the league's offices.

Shane Tamura travels cross-country

Police say last Sunday, Tamura skipped his shift at the Horseshoe casino in Las Vegas, where he did overnight security. Sources say on Monday, a casino coworker purchased part of the assault rifle he later used in the shooting.   

NYPD Commissioner Jessica Tisch said a preliminary investigation revealed Tamura had driven from Las Vegas to New York City in a black BMW. 

He traveled through Colorado on Saturday before passing through Nebraska and Iowa on Sunday. He then entered Columbia, New Jersey, at 4:24 p.m. on Monday. The FBI is compiling a timeline that traces all of his movements as he went across the country, according to CBS News' Pat Milton.

Tamura also had a history of mental health issues in Las Vegas, Tisch said. According to documents obtained by CBS News New York, he refused to show his ID while trying to collect winnings at a casino in 2023. Police say he appeared "agitated" and tried to "grab a security officer." He was arrested for trespass.

Sources say in June of this year, a tipster contacted police after Tamura bought lots of ammunition at a gun show. Officers investigated but found no illegal activity, the source says. His permit remained valid.

Tamura seen outside Midtown office building

Surveillance video shows that Tamura double-parked his car around 6:30 p.m. Monday on Park Avenue between 51st and 52nd streets. He was seen exiting the BMW with an M4 rifle in his hand. 

According to Tisch, the vehicle was registered to Tamura and had a rifle case with rounds, ammunition, magazines and a loaded revolver inside. There was also a backpack and prescription medication for Tamura.     

After exiting the vehicle, he entered 345 Park Ave., a 44-story building with offices for the NFL, KPMG, Rudin Management, and Blackstone.

Inside the lobby of 345 Park Ave.

Once inside the building, he turned right and shot and killed 36-year-old NYPD Officer Didraul Islam. Islam worked for the 47th Precinct in the Bronx and was hired to provide extra security at the building as part of an NYPD program. 

Police then began to receive multiple 911 calls about an active shooter in the building.

"The first call came in at 6:28 for a person walking into the building with a rifle, 6:28, and a couple of seconds later, shots fired. By 6:32 p.m., NYPD officers were on the scene transmitting a 10-13, which means officers needs assistance," New York City Deputy Mayor for Public Safety Kaz Daughtry said.

After shooting Islam, Tamura then shot and killed a woman who was hiding behind a pillar. She was later identified by her employer as Wesley LePatner, an employee of Blackstone.

Gunman takes elevator to 33rd floor

Tamura continued shooting as he walked through the lobby, according to investigators. He walked toward the elevator bank, shooting and killing a security guard who was hiding behind the security desk.

Tamura then waited for an elevator to arrive. He allowed a woman to exit the elevator unharmed.

"We don't know. It could have been someone that looked familiar to him, someone that might look like a relative or something just clicked off in that mentality that he just didn't felt that person was either a threat or a target that was worth engaging at the time," former NYPD member Felipe Rodriguez said.

He then took the elevator to the 33rd floor, where Rudin Management is located.

Once he arrived on the 33rd floor, Tamura walked around and continued firing his gun, killing one person on that floor. That victim was later identified as Julia Hyman.

Finally, Tamura walked down the hall and fatally shot himself in the chest, according to Tisch.

Late Monday night

Following the shooting, Mayor Adams held a news conference with Commissioner Tisch just before 10:30 p.m. on Monday night. The mayor confirmed the number of shooting victims and shared information about slain Officer Islam, who left behind a pregnant wife and two young boys.

"He was an immigrant from Bangladesh and he loved this city. And everyone we spoke with stated he was a person of faith and a person that believed in God and believed in living out the life of a godly person. He embodies what this city is all about. He's a true-blue New Yorker, not only in a uniform he wore but in his spirit and energy of loving this city," Adams explained.

The NFL connection revealed

NFL Commissioner Roger Goodell sent a message to employees Tuesday morning saying that an NFL employee was seriously wounded during the shooting but was in stable condition at a hospital. He also said that anyone who typically works out of the New York headquarters should work from home on Tuesday or take the day off, as the building remained an active crime scene.   

Mayor Adams said on "CBS Mornings" that investigators found a note on the gunman in which he discussed having the brain condition CTE and seemed to blame the NFL, despite never playing professional football. Adams said that after a preliminary investigation, they believed he was targeting the NFL offices but had taken the wrong bank of elevators.

Additional victims identified

Blackstone released a statement Tuesday in which they identified LePanter as one of the shooting victims. She worked in several high-ranking roles at the company over 11 years, including Senior Managing Director of Real Estate in New York. The company remembered her in a statement as "brilliant, passionate, warm, generous and deeply respected within our firm and beyond."

LePanter leaves behind two children and a husband, according to an email from her children's school.

"There are no right words for this unfathomable moment of pain and loss," the Head of the Heschel School, Ariela R. Dubler, and President of the school Ben Archibald said in an email to the community. "She was a uniquely brilliant and modest leader and parent, filled with wisdom, empathy, vision, and appreciation. Quite simply, Wesley made the world – and all of the institutions that she touched, including the Heschel School – a better place." 

The 32BJ SEIU union identified the security guard killed as Aland Etienne. In a written statement they said he was a "dedicated security officer who took his job duties extremely seriously."

"This tragedy speaks to the sacrifice of security officers who risk their lives every day to keep New Yorkers and our buildings safe. Every time a security officer puts on their uniform, they put their lives on the line," 32BJ SEIU President Manny Pastreich said in the statement. "Aland Etienne is a New York hero. We will remember him as such."

Flags ordered to half-staff

Mayor Adams announced on X that all flags in the city will fly at half-staff in honor of Officer Islam and all of the victims, until further notice. 

New York Gov. Kathy Hochul announced that state government buildings will honor the victims by lowering flags until they are all laid to rest. She also called for an assault weapons ban in the wake of the shooting.

"The time to act is now. The American people are tired of thoughts and prayers. They deserve action," Hochul said in a statement.

The investigation into the shooting is still ongoing.