JUST ONE thing is certain: Whoever robbed 92-year-old Joseph Bak on the streets of Roxborough this summer remains a free man.

Police and the District Attorney's Office say that it's because Bak failed to identify his robber in court, despite clearly identifying him on the night of the crime.

But Bak, a retired attorney educated at Penn who reviewed government contracts for the Department of Defense, said that it's because the wrong guy was brought to trial and not only was it the wrong man - he was the wrong race.

Bak believes that police and prosecutors tried to play his age against him when they brought a black, juvenile teen to trial for a crime that he says was perpetrated by a 20-something white man.

"Believe me, I was really flabbergasted when I saw that guy for the first time and I realized they were trying somebody that wasn't the guy who robbed me," he said. "Their excuse is that I got the wrong guy. That I don't realize that's the guy that robbed me."

Assistant District Attorney Ben Baer, who tried the case, and 39th District Police Sgt. William Schmid, who arrested the suspect, said that they were equally flummoxed when Bak got on the stand and adamantly denied that the defendant, a juvenile whose name is being withheld by the Daily News, was not the perpetrator.

"Surprised is an understatement - definitely," Schmid said in an interview. "I was sequestered [during the trial] but when I heard what he said on the stand I was very upset and very surprised."

In the end, Judge Robert J. Rebstock, who presided over the nonjury trial, sided with Bak's testimony and found the defendant not guilty.

But Bak couldn't let the Aug. 31 case go, and came to the Daily News months after to tell his story. He can't speculate on why police and prosecutors "switched defendants."

All he knows is that his first experience as a victim in the legal system he was trained in has left him shaken.

"I got a feeling that the district attorney and particularly the police, they've not only done this but they think it's trivial," he said. "I don't think they appreciate the feeling I had when that guy had his fingers around my throat."

Baer and Schmid said that the case was far from trivial and that it will stick with them for some time to come.

"I'm a prosecutor by choice," Schmid said. "I don't like it when anyone gets assaulted, and I certainly don't like it when 91-year-olds are assaulted in our city.

"But I still believe the right person was arrested for this crime and while good intentioned, the complaining witness was mistaken."

About 8 p.m. on July 12, Bak, during his regular evening walk, had stopped around the corner from his home to peer through a fence on Henry Avenue near Hermit Street to watch players at the Walnut Lane Golf Course.

"To get a good view, you have to put your face against the fence because of all the greenery," he said.It was while he had his face and hands against the fence that Bak felt a squeezing at the back of his neck, he said.

"A guy was choking me," he said. "I was completely surprised. I remember there's only three words the guy said: 'Gimme your wallet.' "

The first time Bak said he saw the man was when he turned around and gave him his wallet.

"I remember the face distinctly, ever since that time I've been looking for it," Bak said. "The man who mugged me was white, no question about it. He was six feet. When he grabbed my wallet I pulled away from him, at that time I noticed that it didn't appear he had any weapon.

"He was strong enough. He grabbed me and threw me towards Henry Avenue. I fell down on my knees, I braced my fall with my hands. As soon as he threw me he started running up along the fence on Henry Avenue."

Bak said that when he got up, he ran into the middle of busy Henry Avenue and started yelling "Police, police!"

He said that an off-duty officer was one of three cars that stopped. He said that he pointed to the assailant and the off-duty officer took off after him in his car.

But during the trial, the off-duty cop, Officer James Wagner, remembered it differently.

Wagner said that he actually saw the assault take place, and that he saw Bak pushed to the ground by a young, black man, whom he identified as the defendant, according to the court transcript.

He doesn't say that he tried to intervene in the assault, but rather, once he saw it take place he made a U-turn, spoke with Bak and went after the assailant on foot, though he eventually lost him, the transcript said.

Bak claims that it would have been impossible for the officer to witness the assault across busy Henry Avenue.

"This thing was so quick and with all the traffic, there's no way he could see," Bak said.

Schmid said that after Wagner called in the assault, he responded to Bak's location, placed Bak in his car and drove around looking for Wagner.

Schmid located Wagner within minutes and transferred Bak to another police car, he said. He was then able to locate the assailant, whom he identified as the defendant in court, within 10 minutes, he said.

He then took him to a parking lot where Bak and Wagner were brought to identify him, Schmid said.

"At that point, he [Bak] was positive about the identification," Schmid said in an interview. "But I was aware he was an older gentleman, sometimes they get a little confused when things like this go on. So I made sure I had the officer come. He said, 'That's definitely the guy.' They were both 100 percent."

Bak remembers it differently. He said that he stayed in the same police car with a responding officer for 2 1/2 hours before he was taken to identify his assailant.

He said that there were three cops present when he identified the man they had in custody, who was white.

"There's no question in my mind I had a good view of this guy and that the guy I identified was this guy," he said. "Not only because he was white, but because of his stature. He was strong."

Bak said that he never asked for the man's name.

"The only identification I have was my seeing him and him robbing me," he said. "If it were to happen again I would say, 'That's the guy. Could you let me have his name?'

"You learn by experience," he said.

One of the most damning pieces of evidence against Bak's version of events is a signed statement by police at 11:20 p.m. that night, at the end of which Bak is quoted as saying: "I told police the guy they stopped was the one that robbed me. I knew it was him because he was black and I saw his face."

Bak said he only read the beginning of the statement, not the end, before signing off on it.

"I didn't read it carefully," he admitted.

He said that between the time of the preliminary hearing, which he claims he was told he did not have to attend, and the trial, he never met with anyone in the District Attorney's Office to discuss the case.

"The first I discussed this case was when I showed up in court," he said. "And there wasn't any discussion. There was never a meeting with the cops or the district attorney in which there was any discussion of the presence of who the defendant would be."

Bak said that he waited in a juvenile courtroom at Vine Street near 18th for hours before Baer approached him. He claims that the assistant district attorney told him before the case that day to point to the guy standing next to his lawyer when he asked him to identify the defendant.

Baer flatly denies the claim.

"Absolutely not," Baer said. "I would never say that. All I asked is if he'd be able to identify the defendant. He told me 'Yes,' with 100 percent certainty.

"I don't tell him what a defendant looks like because that would be unethical."

Baer said that he was also certain that he called Bak before the trial date but could not say whether or not they spoke about the facts of the case.

During trial, Bak was twice asked by Baer if he saw the perpetrator in the courtroom. At one point, he stated "It's not this man," according to the court transcript.

When asked the race of the robber Bak stated: "White, typically white, average white," according to the transcript. When asked if he was sure, Bak replied: "Positive."

He also testified in court that the man whom police apprehended the night of the crime was that man.

In contrast, the off-duty cop Wagner, whom the Daily News was not able to contact, testified that he saw Bak pushed to the ground by the defendant, a young black man, and that there were no white men around.

When asked by Baer if he was sure that the defendant was the "person that accosted the old man," Wagner replied: "I'm positive."

The Daily News was able to locate the juvenile defendant, who, along with his mother, declined to comment on the case.

Schmid, the sergeant who arrested the perpetrator, said that he nabbed the suspect at the Wissahickon Train station and that he was wearing a distinctive shirt that was in the flash information and that he was "heavily sweating."

Schmid said that he brought the perpetrator to a location where Wagner and Bak identified him. In court, he said that Bak "made a positive identification of this defendant right here."

He said that it was rare to have an off-duty officer be a witness to a crime, and rarer still for the victim and the officer to disagree in their testimony.

"For him to say not only is that not him, but we even got the wrong race, it's very odd," Schmid said. "I've never heard of that before. I've witnessed situations where a victim says I'm not sure who it was later on, but I don't know what his motivation was to do that."

Baer said that he vehemently believes that Bak was mistaken because of the testimony of the off-duty officer who witnessed the robbery, Bak's post-incident identification in the presence of a police sergeant and his statement to police.

"In this case, because I had an off-duty officer I didn't need to call him as a witness because I had someone who observed the crime," Baer said. "But he [Bak] was adamant he could make an identification. He was present in court and I saw no reason why he should have not testified."

In the end, it was Bak's testimony that killed the case and Baer found himself arguing against his own victim in his closing.

"My argument is that the complaining witness is mistaken," he said, according to the court transcript.

Judge Rebstock found himself in a quandary.

"What is the court supposed to do when the complainant, the victim, gets up and says that the guy didn't do it, that it was a white guy?," he said. "I particularly asked the older gentleman, 'Was this the guy that did it?' and he said, 'No.' "

Rebstock found the defendant not guilty.