Robert F. Horan Jr. proudly calls himself the "bull" prosecutor of Virginia, meaning that his 35 years as Fairfax County's commonwealth's attorney make him the longest-tenured of all county prosecutors. Those 35 years gave him the patience to wait until this week to file charges against sniper suspects John Allen Muhammad and John Lee Malvo, the confidence to deflect questions calmly at a national news conference Thursday and the experience to direct another high-profile homicide investigation.

Horan has dominated the Fairfax County courthouse for years. Until recently, the chief Circuit Court judge was a close friend and former assistant. His brother is the chief General District Court judge. Many of his former assistant prosecutors have assumed judgeships. And in his quadrennial runs for reelection, he has faced virtually no opposition since 1975.

And Horan, 70, continues to try cases. At an age when many prosecutors might retire or dish off trial work to younger assistants, Horan or his top deputy, Raymond F. Morrogh, handles every high-profile murder case, from arraignment to sentencing. Invariably, Horan sits alone at the prosecution table, often with little more than a pad of paper and never more than one folder of legal briefs.

Standing before a jury, his resonant baritone is tinged with both gravitas and outrage but in quantities that are not overbearing or maudlin. He decides which cases he'll take, and he rarely loses.

"What's always impressed me," said S. Randolph Sengel, the Alexandria prosecutor, "is the guy has an amazing ability to come into a courtroom so well-prepared for his cases that he rarely needs more than a legal pad." Sengel said Horan is "so highly regarded among his colleagues, not just for his trial work but as a scholar. He knows the law, he's studied the law, he keeps up with new developments, and it's really rare you get that combination."

Brett A. Kassabian, a defense lawyer and former Horan assistant, described him as "the dean of prosecutors in the legal community." Kassabian said Horan is a rarity because he continues to try cases and also because he maintains a powerful presence in the courtroom. "I've never seen a person capture a courtroom quite the way he does," Kassabian said.

To be sure, Horan has his detractors. His office differs from others in Northern Virginia by refusing to release copies of police reports to defense lawyers, instead providing a summary of the basic facts. In a current triple murder prosecution, Horan provided the defense with a typed, one-page summary of the defendant's taped statement, rather than the transcript. It was called "Substance of the Oral Statement."

Horan, who did not return phone calls for this article, has said that he follows the letter of the law and that defendants aren't required to provide him with their reports. He also said that withholding reports protects trial witnesses.

Horan is no fan of using DNA to revisit guilty verdicts. In a recent case, he fought a man's attempts to use DNA to overturn his rape conviction, arguing that the man had left no DNA at the scene of the crime. Testing eventually proved that the man did leave DNA, but it also confirmed his guilt.

"I think he thinks he's fair," said Robert C. Whitestone, a veteran Fairfax defense lawyer, said of Horan. "I think defense attorneys by and large have a different view on fairness. I think Horan has a circle-the-wagons mentality when it comes to dealing with defense counsel." But he added: "He's honest. He's got unquestioned integrity. And he's a powerful, persuasive speaker."

Horan was born in New Brunswick, N.J., graduated from Mount St. Mary's College in Emmitsburg, Md., with an economics degree, then spent five years in the Marine Corps. He received a law degree from Georgetown University, sandwiched four years in private practice around two years as an assistant county prosecutor, then was appointed commonwealth's attorney in March 1967. He was elected as a Democrat that November and has won every election since.

High-profile cases are nothing new for Horan. In 1976, he successfully prosecuted James Leroy Breeden, accused of executing four people in a Roy Rogers restaurant freezer in the Landmark area. Also that year, he won the conviction of Arthur F. Goode III, who kidnapped a boy and forced him to watch as he raped and strangled another boy. Goode was executed.

Horan doesn't win on emotion alone. In 1989, he won the conviction of Gary Donahue on first-degree murder charges on circumstantial evidence such as bootprints in the snow and shell casings. And in 1991, he successfully prosecuted Caleb Hughes in the abduction of 5-year-old Melissa Brannen, based largely on hair and fiber evidence.

"He is one of the most capable courtroom lawyers you will ever see," said Peter D. Greenspun, an experienced Fairfax defense lawyer who fought him in the Hughes case and will represent Muhammad.

Although Greenspun agreed that Horan is less cooperative with defense lawyers than other prosecutors are, he sees a larger problem.

"The system of trial by ambush that is allowed by Virginia Supreme Court rules is an unfair system," he said. "If you call the system of limited discovery fair, then he's fair."

Lawyers said Horan carefully considers whether the death penalty is appropriate in each Fairfax slaying and does not seek it often. He obtained it in the 1993 CIA shootings, in which two people died and for which defendant Mir Aimal Kasi is to be executed next week.

But he did not seek it in the case of Keith Gardner, who killed three members of his family in 1999, because other family members did not want it. He is not seeking it in the pending prosecution of Edward Y. Chen, who is accused of killing his parents and brother in 1995, because it might affect witnesses' testimony.

He also seems unswayed by public pressure. In 2000, despite protests from civil rights groups, he declined to file charges against Cpl. Carlton Jones, of the Prince George's County police, after Jones shot a man repeatedly and killed him following a pursuit in Fairfax County.

"I believe that I know a little bit about what it takes to prove a case in court," Horan said. "If you can't prove it in the courtroom, you shouldn't be charging it."

"If you can't prove it in the courtroom, you shouldn't be charging it," says Fairfax prosecutor Robert F. Horan Jr.Prince William Commonwealth's Attorney Paul B. Ebert, who has been in office 34 years, will prosecute sniper suspect John Allen Muhammad.Robert F. Horan Jr., who has served as Fairfax County commonwealth's attorney since 1967, will prosecute John Lee Malvo, the other suspect.