The big break in solving a 1989 hate killing occurred when a childhood friend admitted driving defendant Thomas Gibison to North Philadelphia, where the racist skinhead fatally shot a black man in the head, a federal agent testified yesterday.

"After we interviewed [Craig Peterson on May 1, 2006], the whole world changed," testified Terrence Mortimer, a federal agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Tipped off about the killing in 2004, Mortimer said, he and his partner, FBI agent Scott Duffy, had tried to figure out the identity of the African-American allegedly killed by Gibison "in the late 1980s," and the location of the murder.

They even traveled to Peterson's Vermont home, but he denied the incident. They tried him again in 2006, giving him a subpoena to testify before a federal grand jury, the agent added.

Instead, Peterson cooperated, received immunity and provided details of the 1989 slaying, Mortimer said. Duffy provided the information to Philadelphia Homicide Detective Leon Lubiejewski, FBI-Police violent fugitive task force, so he could research the case.

Lubiejewski testified that he quickly drew up a list of 37 unsolved homicides from January through May of 1989, recorded in the homicide unit's book of that year's slayings.

Based on Peterson's details, the detective testified that he looked for a black male victim about 30 years old, fatally shot once in his head, west of Broad Street in North Philadelphia during the spring, possibly April or May, in 1989.

Only one unsolved murder matched those details: the April 16, 1989 murder of Aaron Wood, said Lubiejewski.

However, he added, the assigned detective who investigated Wood's murder had suspected the slaying was drug-related, according to a note contained in the file.

Until then, the two federal agents had "very, very few details" to go on, testified Mortimer.

Gibison's ex-girlfriend, who was allegedly raped with objects by the defendant, earlier testified that she told the agents about the hate murder, which occurred in the "late 1980s," which she said Gibison often talked about.

Her name is being withheld because of the sexual allegation.

Gibison's attorney, Michael Farrell, hammered Lubiejewski repeatedly for failing to keep the notebook in which he jotted details of the 37 murders.

"My client is on trial for his life," yelled Farrell, who wanted to review the murders to raise reasonable doubt among the jurors.

Lubiejewski said he faxed details of only the Wood murder to the feds, which they included in federal documents.

From the witness stand yesterday, Lubiejewski offered to recreate the list of 37 murders, but Farrell declined.

Dr. Ian Hood, deputy medical examiner, testified that Wood was fatally shot with a .38-caliber bullet between the left temple and forehead - not "between the eyes," which Peterson testified that Gibison had told him.

"The damage to the brain caused instant unconsciousness and death," Hood said. His chance of surviving was "slim to none." He could have been a "human vegetable," he added, or "an organ donor."

Kristin Gerber, an ATF firearms examiner, testified that the bullet that killed Wood was marked with left-hand grooves consistent with the interior of the barrel of a .38-caliber Colt revolver, believed to be the murder weapon.

Under cross examination, Gerber said that left-handed grooves are also inside the barrels of several .38-caliber guns, as well as a .357 Magnum.

Another childhood friend of Gibison, Robert Paolo, an auto mechanic and part-time cop in Berks County, testified that he voluntarily tape recorded Gibison and turned the tapes over to the feds. He also testified that he saw Gibison with a .38-caliber Colt revolver and his racist tatoos.

Transcripts of the tape recordings are to be read into the court record today.

On the night of the murder, witness Jeffrey Jackson testified that he heard what he thought was a car backfiring while walking west on Thompson Street near 26th.

He then saw a bluish or gray new Camaro drive slowly away. Jackson said he did not see the race of the car's occupants. *