His former boss and mentor tried to talk him out of it. His onetime top assistant was "shocked" by the decision.

How, they wondered, could District Attorney Bruce L. Castor Jr. - for eight years the dapper, hard-nosed, summon-the-media face of Montgomery County law enforcement - ever be content as a budget-grinding county commissioner?

Pennsylvania's most populous suburban county is about to find out. After 22 years in the District Attorney's Office - two-thirds of them as top dog or second in command - Castor will move across the street from the Norristown courthouse to the commissioners' suite next month.

With him passes a provocative era marked by big-headline, mostly successful prosecutions. And by the omnipresence of the telegenic Castor on the airwaves - all Bruce, all the time.

"I will miss it a lot," Castor, 46, said last week in an office bearing no signs of imminent departure. But, he said, he has run out of challenges.

"I have accomplished everything that I think I can as district attorney," Castor said. "There are no more mountains that I want to climb. I think I am leaving at the top of my game."

He was the top vote-getter of the three commissioners elected last month. His veteran first assistant, Risa Vetri Ferman, won the district attorney's race.

For Castor, friends predict a difficult transition.

"I tried to tell him," said his fiery predecessor as district attorney, Michael D. Marino, who spent four unhappy years as a commissioner before switching to county solicitor. "He didn't listen."

A self-described "policeman who wears a suit," Castor is exiting a familiar, black-and-white world where blood flows, innocents die, and bad guys are brought to justice. And where his word is final.

He is entering a grayer, give-and-take political realm where there is no way to divvy up a half-billion-dollar annual budget and make everyone happy. Where the well-connected queue up for contracts to spend the county's money, manage its property, or relocate its sewage-treatment plant.

It's not exactly an adrenaline pump for someone who took down the likes of Caleb Fairley, the goth misfit who strangled a young mother and her toddler in Collegeville; Craig Rabinowitz, the stripper-obsessed schlub who drugged and strangled his wife in their Main Line home; and Guy Sileo Jr., the diminutive chef who executed his business partner at the General Wayne Inn in Merion.

"I told Bruce I thought he was making a big mistake," said Richard Winters, a former county solicitor. "The commissioners' office is like running a huge household, with so many people screaming for money and attention. It's not as glamorous as being in the D.A.'s office."

Alan M. Rubenstein, the longtime, shoot-from-the-hip district attorney in Bucks County, can speak to that. Now a Common Pleas Court judge, he said he had needed "a good six months" to decompress from the pace and limelight that he and Castor so loved.

"It went from 200 miles an hour to 15 miles an hour," Rubenstein said. "From driving through the Bonneville salt flats to driving through a school zone."

Like Rubenstein, Castor was far more than a guy in French cuffs and monograms who played to the cameras. He was a highly effective prosecutor, a detail fanatic whose courtroom skills were widely admired.

"Bruce is in the top 1 percent of prosecutors I've seen in action," said lawyer Timothy Woodward, a longtime homicide detective who later served as Castor's first assistant. "Bruce was so good, you kind of took it for granted. I'm shocked that he's leaving, because he loved it so much."

Castor - whose ancestry includes a Philadelphia mayor (Thomas B. Smith, 1916-20), a president of Breyer's Ice Cream (Clyde H. Shaffer), and the Swiss-born namesake of Philly's Castor Avenue - said he had planned to stay only five years when he joined the District Attorney's Office in 1986.

The work enthralled him, though, and Marino, elected in 1988, promoted him rapidly. "He was a superstar. You could see it," Marino said.

Dubbed the "Golden Boy" by some courthouse wags, Castor became Marino's top assistant at age 32. Thorough to a fault, he insisted that detectives keep investigating cases even after arrests were made.

"He used to drive me crazy with preparation," Woodward said. He recalled once mashing Castor in the face with a door as Woodward stormed out of a police interrogation room. That's how closely Castor had been eavesdropping from the hallway.

Even the one man who saddled him with a big loss in the courtroom - a man Castor openly dislikes - strongly praises him.

"He has never lied to me. His office is an honorable office, a fine office to deal with," said Frank DeSimone, who won acquittal for Patricia Swinehart, accused of masterminding the murder of her husband for insurance wealth.

Castor's peers thought enough of him to elect him the current president of the Pennsylvania District Attorneys Association.

Still, he said, it was time to go. He looks forward to entering private practice - forbidden for a prosecutor - and said he had feared a Democratic takeover of county government had he not run.

"I thought that would be a disaster for the D.A.'s office," the lifelong Republican said. A Democratic majority "would have done whatever they could to tone down my profile and cut our budget."

In last month's election, Democrats did win county row offices long held by the GOP, but Castor and incumbent Jim Matthews retained party control of the commissioners.

With former U.S. Rep. Joseph Hoeffel, the new Democratic commissioner, the board could be a volatile mix. Matthews and Hoeffel clashed bitterly with Castor on the campaign trail: Hoeffel called him "Bruce Almighty," and Matthews said Castor's ego was so big "it could float the Titanic."

Both say that those days are past, that they expect to work well with Castor.

"He has cautioned us that he is an autocrat, that he's not used to working together with people, so bear with him," Matthews said.

"He's aware. But he will learn quickly."

Notable Castor Cases

Thomas W. Hawkins Jr.:

Hawkins was convicted and sentenced to death in 1991 for murdering and raping his 14-year-old niece, Andrea Thomas, in her West Pottsgrove Township home. After a successful appeal, he was convicted again in 1994 and is on death row.

Patricia Swinehart:

Charged a decade later with arranging the 1982 stabbing death of her estranged husband, Swinehart was acquitted of murder by a jury in 1994. Pottstown developer David Swinehart had been slain at the end of his driveway by a group of men including two of his nephews - one of whom was having an affair with Patricia Swinehart.

Caleb Fairley:

Fairley was convicted in 1996 of strangling Lisa Marie Manderach, 29, and her 19-month-old daughter, Devon, as they shopped in a Collegeville children's clothing store owned by Fairley's family. A deal was struck to spare Fairley's life if he directed police to the mother's missing body; he is serving two consecutive life sentences.

Craig Rabinowitz:

The latex-glove salesman pleaded guilty, just before trial in 1997, to strangling his lawyer wife, Stefanie, 29, in their Main Line home. Cash-strapped from lavishing money on a Philadelphia stripper, Rabinowitz dumped the body in a bathtub, hoping to make the death look accidental and collect a $1.8 million insurance policy. He is serving life in prison.

Guy Sileo Jr.:

Sileo was convicted of first-degree murder in 2001 for fatally shooting business partner James Webb, 31, in a third-floor office of the financially struggling General Wayne Inn in Lower Merion in 1996. He is serving life in prison.

Rafael Robb:

The University of Pennsylvania professor pleaded guilty Nov. 26 to bludgeoning his wife, Ellen, 49, last December with an exercise bar in the kitchen of their Upper Merion home. He is awaiting sentencing next year.

Contact staff writer Larry King

at 215-345-0446 or lking@phillynews.com.