The impact hurled fragments of the helicopterover the roof and onto the ground.

"There were two big pieces and a couple hundredpieces on the ground," said Steven M. Turner ofRoxbury, who witnessed the crash as he sat in abus on the Mass. Ave. Bridge. "[It was] just onebig mess."

"It was so mangled it no longer looked like ahelicopter," said Michelle A. Kamin, anoffice-worker who watched the rescue team from heroffice on the other side of the street.

Gasoline from the twisted helicopter wreckagewas gushing onto the roof and into the river,bringing with it the danger of a massiveexplosion, witnesses said.

"When we realized how much gasoline was beingspilt on roof, we didn't want any more [people] on[the roof] than necessary," Barber said. The otherrescue workers stayed on the ground to keep thegrowing crowd away from a possible explosion.

Officials from the state's EnvironmentalProtection Agency worked to contain the spill asfire-fighters sprayed flame-retardant foam intothe building.

Above them, the four team members raced to pullthe helicopter's crew out of the wreckage butfound no vital signs on any of the four victims,Barber said.

"They looked like clumps, they didn't look likebodies," Kamin said.

Other MIT emergency medical technicians hadarrived while the crew was getting on the roof.

State police and Cambridge police and firedepartment personnel followed quickly.

"They got there almost immediately," Kaminsaid.

Barber said that quick work by the emergencyresponse personnel kept the scene from becomingchaotic.

"It was congested...[but] organization fellinto place relatively quickly," Barber said.

Ironically, when they witnessed the crash,Barber's team had been taking a break frompracticing emergency procedures in a nearbybuilding.

"We were talking, ready to finish and get backto our job," Barber said. "Ten minutes either waywe wouldn't have been there."

Marios V. Broustas contributed to thereporting of this story.