Prosecutors unsuccessfully moved to treat their own mentally and physically disabled witness as hostile when his testimony unexpectedly bolstered the defense of his friend and co-worker, William Rapetti, the master rigger on trial for manslaughterand negligent homicide in a 2008 Manhattan crane collapse that killed seven.

John Della Porta, who was a construction worker on March 15, 2008, was called for the prosecution because he testified in an interview with the district attorney’s office that before the crane crashed, no one inspected the nylon slings used to attach the six-ton collar of the 200-ft. crane to its mast. The condition of the slings has been the center of the prosecution’s case, arguing that they were old, sun-faded and torn.

The prosecution’s case hinges on the notion that Rapetti supported the tower crane with only four damaged slings instead of eight new ones when it was being “jumped,” or extended. But several of their witnesses have contradicted this argument and Della Porta retracted his original statements on the stand.

Della Porta on Tuesday claimed he had seen Rapetti “destroy brand new slings that were barely nicked or ripped” and “was sure” the slings were inspected before use. Before he took the stand, the general manager of crane’s manufacturer Favco testified that his company never sent a recommendation to use eight slings to any individual or company until after March 15, 2008. The manufacturer’s recommendation has also been central to the prosecution’s case.

Della Porta blamed the apparent inconsistency on his severe amnesia, saying he had “extremely limited recall” because of his massive head injuries suffered during the accident. He said he also went blind in one eye, injured his back, and fractured his shoulders, legs and hips

Prosecutors argued that their witness’s memory lapses showed “reluctance and bias” to say anything negative about his decades-long friend Rapetti, who faces 27 years in prison if convicted.

Judge Hayes denied the prosecution’s motion to treat Della Porta as hostile because he did not make his pre-trial statements to the district attorney while under oath.

Last week, the worker responsible for handling the slings described taking new slings out of the plastic before the jump, and the site supervisor confirmed he ordered them at Rapetti’s request.

The prosecution’s sling experts are expected to testify on Wednesday and the defense is supposed to begin calling its witnesses as early as Friday.