The incident occurred when a third collar was being attached to the year-old Favco 440 after it had been climbed, according to James Lomma, president of crane owner New York Cranes. He said that the collar slipped, and knocked out two lower collars that attached the tower crane to the building. Without any connections to the building, the crane toppled over. The crane was about 200ft (61m) high when the accident occurred. The crane fell on top of nearby buildings on 50th Street.

Lomma added that he did not know why the collar slipped, but he said that the crane climbing operations were carried out by a construction subcontractor. Investigators are pursuing a theory that one of the fabric slings holding the collar snapped.

Seven people are now known to have been killed in the accident, six of whom were construction workers. They are: Wayne Bleidner, 51, of Pelham; Brad Cohen, 54, of Farmingdale; Anthony Mazza, 39; and Aaron Stephens, 45, of New York City; Santino Gallone, 37, of Long Island; Clifford Canzona, 45, of Long Island, according to reports in the Associated Press and the New York Daily News.

The last person killed, Odin Torres, 28, of Hialeah, Florida, was in a nearby building that was crushed by the falling crane.

According to the New York Daily News, two of the three critically injured victims have improved, and are now in fair condition. Ten people remain hospitalised.

Buildings engineers and inspectors have been supervising the safe removal of the crane cab from the collapse site at 305 East 50th Street, and the 10 mast sections that destroyed the four-storey building on this site. They have also supervised removal of three steel beams supporting the crane on floors 3, 9 and 18 of the construction site at 303 East 51st Street.

At 300 East 51st Street, the other work site, two mobile cranes, positioned at East 51st Street and 2nd Avenue, have lowered the crane’s boom to the street level, according to the New York City Office of Emergency Management. Once the crane’s boom was lowered, workers began dissembling it. This work was allowed to proceed after the bolts on the crane’s mast were thoroughly analyzed by engineers and found to be intact, the agency said. Operations will continue as the crane’s mast is removed from the site and the debris pile is stabilized.

Buildings engineers and inspectors have been supervising the safe removal of a piece of the tower support that speared the roof building at 306 East 50th Street and passed through the shared wall with 308 East 50th Street. Both of these buildings remain vacated due to the structural damage sustained during the accident.

The Buildings Department continues to work with the Police Department to recover and secure the parts needed for the forensic investigation into the accident. Once these parts are recovered and secured, they are being sent to a testing laboratory off-site for analysis.

Buildings forensic engineers have confirmed at least seven buildings sustained damage during the accident. Portions of the roof and top two floors of a four-storey building at 301 East 50th St/944 2nd Avenue collapsed when the crane hit it.

New York safety authorities allowed some nearby residents to return to their homes on Tuesday.