BOSTON -- A small plane carrying a cancer patient from Long Island to Boston went into a nosedive and crashed Tuesday in a grocery store parking lot, killing all three people on board, authorities said.

The Federal Aviation Administration said the plane was part of Angel Flight Northeast, a network of local pilots who volunteer to run medical flights at no charge to the patients.

Easton police identified the pilot as Joe Baker, of Brookfield, Conn. FAA officials said Tuesday's flight originated in Westhampton, N.Y., and Camerlin said Baker had joined the network in November.

The couple was identified by authorities as Robert Gregory, 43, and Donna Gregory, 37, both of Riverhead, N.Y.

The plane crashed at about 10:20 a.m. Tuesday at the Highlands Plaza near the Hannaford grocery store. The plaza is located on Robert Drive off Route 106.

"What we can tell is there were three fatalities in the aircraft. As to what happened, as to what may have transpired prior to that, we don't know at this point," said Wally Bunker, of the Massachusetts Aeronautics Commission.

Witnesses Describe Seeing 'Big Ball Of Flames'

Easton Deputy Police Chief Allen Krajick, a pilot himself, said that he saw the plane flying very low moments before the crash and knew the aircraft was in trouble.

"I knew he was in trouble, obviously, at that altitude and attitude nose-down like that. That is not a maneuver they would ever do in an area like this, on a day like this," he said.

Witnesses said people on the ground ran for cover moments before the plane crashed into a remote corner of the paved parking lot. The plane, a single-engine Beech Bonanza, burst into flames when it hit the ground, witnesses said.

"People were running in the parking lot like they heard the plane, and they were running before it hit. I don't believe anybody on the ground was hurt," said witness Patty Desgrosseillies, the manager of the nearby Bank of Easton.

"I saw a plane just going very straight, no landing gear, and it just nose-dived. In one second it completely blew up with one big ball of flames," said witness Jean Ryan.

Some witnesses said it looked as though the pilot tried to make an emergency landing on the parking lot.

"I saw the plane going around, and I think he was trying to land ... they were going to use (the parking lot) to land," said witness Phyll Aguian.

"From when I first heard it to when I saw it, (the pilot) did maneuver, he turned. But I don't know what was going inside the cockpit at the time," Krajick said.