A state police helicopter crashed into a Harvard University boathouse Wednesday morning, killing all four people aboard.

The helicopter flew westward over the Massachusetts Institute of Technology campus before it crashed into the boathouse on the banks of the Charles River, witnesses said."I looked up and I saw it coming down, I saw it coming down fast," said Scott Farrar, who was at work at nearby Kwik Copy. "I saw a puff of snow or smoke when it hit the building."

"It wasn't wiggling or on fire or anything like that," said another witness, Doug Kramer. "It looked like it was in control."

After the crash, the French-made Aerospatiale helicopter could be seen lying on its side with its tail shorn off but both rotors intact. The one-story, flat-roofed building did not appear to be seriously damaged.

University officials said the building was unoccupied at the time of the incident. The four victims, all from aboard the helicopter, were two state police officers and two employees of AT&T, police said.

Robin S. Ayre, AT&T spokeswoman, could not immediately confirm that anyone from her company was on board. The helicopters are used for various things, from rescues to surveillance to transporting dignitaries, police said.

Tom Fiddaman, 29, an MIT student, said he ran to call 911 when he saw the crash, then ran to the boathouse and found other would-be rescuers already there.

The helicopter, which was roughly 5 years old, had just left the Nashua Street helipad about two miles away, state police spokesman Grant Moulaison said.