Cops say they arrested the man who allegedly killed the potential witness in the WHITEY BULGER trial. Cause of death? Poisoned ice coffee.

Law enforcement say a Massachusetts man is charged with attempted murder for allegedly poisoning the iced coffee of a man who fed had hoped would testify at James "Whitey" Bulger's trial.

Stephen "Stippo" Rakes' body was fgund by a jogger July 17 in the woods in the Boston suburb of Lincoln.

 Middlesex County District Attorney Marian Ryan told media  that William Camuti,69, of Sudbury owed Rakes a vast amount of money and seemingly acted alone.

A murder charge has not been officially filed  because the M.E. is still conducting additional forensic testing and is waiting for results.

Prosecutors contend the murder vic Rakes and his former wife were forced to sell Bulger their South Boston liquor store in 1984 to use as a headquarters for his nefarious gang.

Reportedly, Rakes had been forward to testifying against Bulger but learned from  prosecutors the day before he would not be called to the stand.

He ended up dead anyway.