In the film "Die Hard", how does John McClane finally get the attention of Sgt. Al Powell who is at the plaza?

In the 1988 film "Die Hard", John McClane (Bruce Willis) finally get the attention of Sergeant Al Powell (Reginald VelJohnson) who is at the plaza by dropping a terrorist body on Powell's patrol car. Sergeant Powell is an off-duty police officer who gets called into work to investigate a potential hostage situation at Nakatomi Plaza. Powell then becomes a central character in the conflict, and a source of moral support for protagonist John McClane. McClane says "Welcome to the party."

In the film at the beginning, New York City Police Department Detective Lieutenant John McClane is seen traveling to Los Angeles to attend a Christmas Eve party at Nakatomi Plaza, the workplace of his recently separated wife Holly Gennero (Bonnie Bedelia). She and their two children, Lucy and John Jr., live in Los Angeles.

Nakatomi Corporation employees including Holly are taken hostage in a bid by terrorists to conceal the theft of bearer bonds under the guise of a failed terrorist act. McClane evades detection of the bad group and hides throughout Nakatomi Plaza, systematically killing the group members as he attempts to disrupt their plot.

The criminal leader, Hans, aware of John's presence and his name, eventually identifies Holly as John's wife and takes her as his personal hostage. At the end of the film, a badly injured McClane locates Hans and Holly near the vault on the 30th floor. Hans is shot by McClane and falls to his death after stumbling backwards through a window.