Police in New York City say they are looking for a man called Frank R James in relation to an attack on a rush-hour subway train in Brooklyn in which at least 10 people were shot.
They described him as 62 years old, with addresses in Philadelphia and Wisconsin.
"He is a person of interest in the shooting that took place on the N train in Brooklyn Tuesday morning," police said on Twitter.
A $US50,000 reward is being offered for information leading to his arrest.
Warning: This story includes graphic images.
Police said keys found at the scene of the attack led them to an abandoned rental van which was found about 6 kilometres away.
Five people were in critical condition but expected to survive and at least 29 in all were treated at hospitals for gunshot wounds, smoke inhalation and other conditions after the attack. There were no deaths.
Gunman set off smoke grenade, then opened fire
The gunfire erupted during morning rush hour on a Manhattan-bound N train that pulled into 36th Street station in the Sunset Park neighbourhood, about a 15-minute ride from Manhattan and predominantly home to Hispanic and Asian communities.
A gunman in a gas mask and wearing a construction vest set off a smoke grenade and then started shooting.
A scene of horror unfolded as frightened commuters ran from the train and others limped out of it.
"My subway door opened into calamity. It was smoke and blood and people screaming," eyewitness Sam Carcamo told radio station 1010 WINS.
Smoke poured out of the train car as the door opened, he added.
The FBI said a joint terrorism task force had joined the investigation.
Earlier, Police Commissioner Keechant Sewell said the attack was not being investigated as terrorism, but that she was "not ruling out anything."
Authorities found a 9mm semi-automatic handgun at the scene of the shooting, along with extended magazines, a hatchet, both detonated and undetonated smoke grenades, a black garbage can, a rolling cart, petrol and the key to a U-Haul van which was later found abandoned in another part of Brooklyn, Chief of Detectives James Essig said.
Commissioner Sewell said the gunman fired 33 shots.
Investigators believe the gunman's weapon then jammed, preventing him from continuing to fire, officials said.
Police said they believed the gunman acted alone and immediately fled the crime scene.
Allan Lee was running his business, Cafe Nube, when half a dozen police cars and fire vehicles suddenly converged on the block that contains the 36th Street station.
"Then they started ushering people that were on the block to the adjacent block and then closed off the subway entrance," Mr Lee said.
Citizens' cameras capture chaos
One passenger's video, shot through a closed door between subway cars, shows a person in a hooded sweatshirt raising an arm and pointing at something as five bangs sound.
In another video, smoke billows as people pour out of a subway car, some limping.
"Someone call 911!" a person shouts.
Other video and photos from the scene show people tending to bloodied passengers lying on the platform — some amid what appear to be small puddles of blood — and another person on the floor of a subway car.
Passenger Juliana Fonda, a broadcast engineer at WNYC-FM, told news site Gothamist that passengers from the car behind hers started banging on the connecting door.
Brooklyn resident Yayha Ibrahim said he saw people running from the 36th Street station, and decided to walk down into it to see what was happening.
"I saw a lady, she was shot right in her leg and she was screaming for help," he said.
Rescue workers "did a good job of coming quick and fast, and the ambulance came in and they took her."
Reports of security cameras malfunctioning
The attack prompted officials to increase policing at transportation hubs from Philadelphia to Connecticut.
The Metropolitan Transportation Authority (MTA) announced last year that it had put security cameras in all 472 subway stations citywide, but the cameras apparently malfunctioned in the station where the train arrived, New York City Mayor Eric Adams told WCBS-AM.
MTA system chief Janno Lieber told TV interviewers he did not know why the cameras malfunctioned, but said police had "a lot of different options" from cameras elsewhere on the subway line to get a glimpse of the shooter.
New York City has faced a spate of shootings and high-profile incidents in recent months, including on the city's subways.
One of the most shocking was in January, when a woman was pushed to her death in front of a train by a stranger.
Mr Adams, a Democrat a little over 100 days into his term, has made cracking down on crime — especially on the subways — a focus of his early administration, pledging to send more police officers into stations and platforms for regular patrols.
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