Subway gunman Bernhard Goetz and his girlfriend attended the opening of a murder trial of a woman who claims she stabbed her abusive boyfriend to death in self-defense. ``This trial should not be happening,'' Goetz said after opening arguments in state Supreme Court, the state's trial-level court, in Manhattan on Thursday. Damian Pizarro is accused of killing her boyfriend, Emerson Gaylor, on Aug. 19, 1986. Her attorney, Peter Neufeld, said Gaylor began abusing Ms. Pizarro after she became pregnant with his child in 1984. Goetz' girlfriend, Lisbeth Theisen, said the couple decided to attend ``to show support'' for Ms. Pizarro. Goetz is free on bail while appealing his conviction in the shooting of four teen-agers on a subway train in December 1986. Goetz, who maintained he fired because he felt threatened, was convicted last June on a weapons charge.