Retired Mt. Lebanon police Officer James Patrick O'Donnell knew that his longtime colleague, Patrolman Daniel Rieg could be in trouble when he heard the commotion on Rieg's police radio on the night of May 26, 2002.

Rieg was calling for backup because the dispute was rapidly escalating. Edward Constant II, 60, and his wife, Susan Constant, 48, were drunk, belligerent and verbally abusive to the two officers. Part of Edward Constant's profane tirade was overheard over the radio.

"I'm coming Code 3, Dan," O'Donnell responded, meaning that his emergency lights and siren were blaring as he sped from another part of Mt. Lebanon.

O'Donnell said as he rushed to the scene, he heard the report over his police radio, "Officer shot."

"It seemed like it took me forever to get to Danny because I knew he was hurt," O'Donnell testified yesterday, the second day of Constant's trial on charges that include attempted murder of a police officer.

"I was pushing that vehicle as hard and as fast as it would go to get to Danny," O'Donnell said.

Rieg and Officer Jeffrey Kite had been first to respond to what had been called in by a neighbor as a boisterous domestic dispute at the home of the former Carnegie Mellon University professor.

In less than a minute, from the time of that radio transmission to the moment O'Donnell arrived at the scene, Rieg had been shot in the chest, saved only by the bulletproof vest he had been wearing.

Upon arrival at Piper Drive where the Constants lived, O'Donnell said he yelled for Rieg, who directed the backup officer to the front lawn of the suspect, where he found Constant lying on his back.

Constant had been wounded in the buttocks by one of the dozen of shots returned by Rieg.

Susan Constant was not injured.

O'Donnell said he eventually noticed Rieg and Kite crouched behind Rieg's police car that was parked in front of Constant's home.

As Constant lay on his back with his arms extended beyond his head, Susan Constant sat on the grass beside him, tending her husband. The .44-caliber revolver Constant had used lay near the man's right hand, O'Donnell said.

O'Donnell said that he retrieved the suspect's weapon, confirmed that all six rounds in the chamber were spent, and stowed it in the trunk of his police car.

The jury of nine women and three men, plus two alternates, were shown photos of Rieg's wounds yesterday.

The bullet, though it did not pierce the protective vest, dimpled it enough to cause an open wound on the left side of the officer's chest.

Rieg, a 16-year police veteran, remained off the job until the fall of 2002 when he had recovered from that wound as well as the large contusion to his left hip, stiffness and soreness to his neck and powder burns from the close-contact gun shot.

Defense attorney Paul Boas has said he will try to show that Constant, in his drunken stupor, believed he was acting in self-defense and to protect his wife.

O'Donnell, under questioning by Assistant District Attorney Bruce Beemer, said that the Constants at first ignored his requests to raise their hands to show they were not armed. He said the couple remained verbally abusive even during their arrests.

O'Donnell said that Edward Constant never expressed any concern at that time for his wife's safety from the perceived threat by police. O'Donnell retired last fall after 20 years on the force.

Constant, who has since taken early retirement, was a history professor who specialized in the relationship between scientific progress and radical technological change. He remains free on bail.

He is charged with two counts each of attempted homicide and aggravated assault on police officers and one count of simple assault.