PHOENIX — The 22-year-old man who faces charges he tried to assassinate Rep. Gabrielle Giffords in a Tucson shooting rampage that left six people dead is not cooperating with law enforcement officials.

Sheriff Clarence Dupnik said Jared Loughner is not cooperating and told ABC News the suspect had said “not a word” to investigators.

Loughner makes his first court appearance at 4 p.m. Butler time today.

Public defenders are asking that the attorney who defended Oklahoma City bombing conspirator Timothy McVeigh and “Unabomber” Ted Kaczynski defend Loughner.

The hearing in Phoenix comes just a few hours after President Barack Obama leads the nation in a moment of silence for the victims and their families. Obama will observe the moment of silence at 11 a.m. EST with White House staff on the South Lawn.

Giffords, 40, is in intensive care at a Tucson hospital after being shot in the head.

Neurosurgeon Dr. Michael LeMole of Tucson’s University Medical Center, appearing this morning on CBS’s “The Early Show,” said, “the best way to describe her this morning is that she’s holding her own.”