Authorities identified the pickup driver as Volodoymyr Zhukovskyy, 23, an employee of a Springfield, Massachusetts, company called Westfield Transport.
Zhukovskyy survived the accident and has not been charged, authorities said, but they didn't release details on his condition or his whereabouts. A phone listing for him couldn't be found, and Westfield Transport didn't immediately return a phone message.
The National Transportation Safety Board is among the agencies investigating. Authorities said they're asking for the public's help in the form of videos, photos or other information about the accident or the vehicles involved.
"This is one of the worst tragic incidents that we have investigate here in the state," New Hampshire State Police Col. Chris Wagner said at a Saturday news conference in Lancaster. "It's going to be a very lengthy investigation."
A 2016 Dodge 2500 pickup truck towing a flatbed trailer of the kind used to haul cars collided with the riders around 6:30 p.m. Friday on U.S. 2, a two-lane highway in nearby Randolph, police said. Randolph is about a two-hour drive north of Concord, the capital, and a three-hour drive from Boston.
Along with the seven dead, state police said three additional people were taken to hospitals. Two of them were released Saturday. Police did not provide names.
The crash sent shockwaves through New England's community of motorcycle enthusiasts and military veterans, which sometimes overlap. The crash involved members of Marine JarHeads MC, a motorcycle club in New England that includes Marines and their spouses.
"When something like this happens, we all feel it," said Cat Wilson, who organizes a motorcycle charity event in Massachusetts and is a friend of some of the crash victims. "There is no tighter community than our biker community."
The road reopened Saturday, and skid marks were still visible on the road, which has mountains and fields as a backdrop. A patch of burned grass remained.
Bill Brown, a 73-year-old military veteran and motorcyclist, arrived at the scene near a gentle curve in the road to plant flags, calling the victims "brothers in arms" and vowing to keep riding.
Members of the motorcycle community are already organizing help for the victims' families, Wilson said. A memorial in nearby Berlin was planned for Saturday evening.
The pickup truck was on fire when emergency crews arrived. Witnesses described a "devastating" scene as bystanders tried to help riders lying in the road.
Update: Multiple fatalities have been reported as a result of a crash involving motorcycles and a pickup truck on Route 2 in Randolph: https://t.co/jRXu5YaPKK— WMUR TV (@WMUR9) June 22, 2019
📸: u local/Miranda Thompson pic.twitter.com/2O8VTNWtQu
A photo posted by WMUR-TV showed motorcycles and wreckage scattered across the highway and a truck on the shoulder in flames.
The crash created a chaotic scene in the town of about 300 people.
"There was debris everywhere," said Miranda Thompson, 21, of Manchester, who was several cars back and recalled seeing a truck in flames on the side of the highway and six motorcycles.
"People were in the grass," she said. "There were people putting tourniquets on people, trying to make sure they didn't move."