The gunman who killed eight people at a FedEx facility in the US city of Indianapolis was a former employee, the company says.
Police named the suspect as 19-year-old Brandon Hole, who last worked at the company in 2020.
He began shooting "randomly" almost immediately after exiting his car, according to police.
Seven people were also injured and the gunman apparently killed himself before police arrived, officials say.
This is the latest incident in a recent increase in mass shootings across the US.
At least four of those killed were members of the Sikh community, according to local media. Gurinder Singh Khalsa, a leader of the local Sikh community, told Reuters news agency that the FedEx facility was known for employing members of the community who did not speak fluent English.
A statement from FedEx chairman and CEO Frederick Smith described the incident as a "senseless act of violence".
"First and foremost, I want to express my deepest sympathies to the families, friends, and co-workers of those team members. Our priority now is in responding to the situation on the ground and helping our team members and law enforcement," the statement said.
Ordering flags to be flown at half-mast, President Joe Biden described the recent mass shootings as a "national embarrassment".
"It has to end," Mr Biden said. "Every day there's a mass shooting in the United States if you count all those who were killed out in the streets of our cities and our rural areas, it's a national embarrassment and it must come to an end."
The attack began around 23:00 local time (03:00 GMT) on Thursday in Indianapolis, Indiana - the state capital and its largest city.
In a news conference on Friday, city officials said no motive had been established yet, and noted that one may never be determined.
"We'll never really know all the ins and outs of why this occurred, but we'll try our best," said police chief Randal Taylor.
Craig McCartt, the deputy chief of criminal investigations, said that the gunman began firing as soon as he arrived at the building.
"This suspect came to the facility and when he came there, he got out of his car and pretty quickly started some random shooting outside the facility," he said.
"No confrontation or argument, he just appeared to randomly start shooting," he added.
Four people were found dead outside the building, and another four inside.
The attacker, who appeared to have shot himself "minutes" before police arrived, was also found inside the facility.
"When officers arrived they found a very chaotic and active crime scene," Mr McCartt said, adding that they believed the gunman used a rifle during the attack.
Mayor Joe Hogsett paid condolences to the victims and called for Americans to tackle the "scourge of gun violence that has killed far too many in our community and in our country".
He also called for people to fight against "the assumption that this is how it must be and we might as well get used to it".
"We need the courage that compels courageous acts."
The FBI, which is assisting in the investigation, has been searching a residence in the area, officials said, but they refused to answer whether it was the suspect's home.
A statement from FBI Indianapolis Special Agent in Charge Paul Keenan, said a shotgun was seized from the suspect in 2020 after his mother told authorities that he might try to get killed by a law enforcement officer, CBS News reports.
The suspect was interviewed last April and "no racially motivated violent extremism ideology was identified during the course of the assessment," Mr Keenan said.
'He was firing in the open'
Local media quoted FedEx worker Jeremiah Miller as saying he had seen the gunman firing.
"I saw a man with a sub-machine gun of some sort, an automatic rifle, and he was firing in the open. I immediately ducked down and got scared," he said.
This is the third mass shooting in Indianapolis this year. Five were killed, including a pregnant woman, in a shooting in January. In March, three adults and one child were killed after an argument broke out over a coronavirus stimulus cheque.
The Gun Violence Archive puts the number of gun violence deaths from all causes at 12,395 so far this year in the US, of which 147 were in mass shootings. Last year saw a total of 43.549 deaths, and 610 in mass shootings.
Last week, President Joe Biden announced his first steps since taking office to tighten gun controls following a series of mass shootings.
It includes efforts to set rules for certain guns, bolster background checks and support local violence prevention.