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Seeking to reduce public expectations after weeks of painstaking investigation have yielded little new public information, federal officials caution that new arrests are not likely soon in the Oklahoma City bombing case.

Although they are still searching for the suspect known as John Doe No. 2, officials now doubt whether he was actively involved.

In contrast with the first weeks of the investigation, which were marked by a series of spectacular breaks, investigators now are focusing on the meticulous and less visible work of presenting evidence to the 23 grand jurors at Tinker Air Force Base in Oklahoma.

Under law demanding a speedy trial, prosecutors have until June 12 to indict Timothy McVeigh, the first man arrested for the bombing that killed 168 people and injured about 500 others.

But a U.S. Justice Department official said Friday that the government will ask that the deadline be extended until “sometime this summer.” Such continuances are not unusual in complex cases.

McVeigh and his ex-Army buddy Terry Nichols are being held separately in solitary confinement at the Federal Correctional Institute in El Reno, Okla.

At a two-hour detention hearing Friday in the prison visitor center there, U.S. District Judge David Russell denied Nichols’ motion to be set free on bail, ruling with prosecutors that he was a flight risk.

Nichols’ attorney, Michael E. Tigar, contended that Nichols was being harrassed and treated unfairly in jail.

Meanwhile, authorities continued to question close associates of McVeigh and Nichols.

Prosecutors reportedly have enough evidence to charge another Army buddy, Micheal J. Fortier, with being a “second-tier” conspirator in the bombing. A government official confirmed reports that Fortier took part in test blasts and may have had prior knowledge of the plot.

Fortier reportedly told authorities that he and McVeigh traveled to Oklahoma City to inspect the Alfred P. Murrah Federal Building before the bombing.

An official confirmed Friday that authorities have rejected a plea-bargain offered by Fortier’s attorneys, refusing to grant him immunity or a reduced sentence until he provides more details about the plot. Fortier of Oatman, Ariz., is not in custody and has not been charged with a crime.

McVeigh’s sister Jennifer was questioned extensively by authorities but is not considered a suspect, a federal official said Friday. She reportedly shares many of her brother’s anti-government sentiments and was in contact with him in the months before the blast. She has cooperated with authorities.

Steven Garrett Colbern, a chemist who knows McVeigh, was scheduled Friday to be moved to a Los Angeles federal prison. Colbern is charged with being a fugitive felon in possession of a firearm and also with resisting arrest when he was apprehended by U.S. marshals in Arizona on May 12.

Colbern’s attorney John Hannah has told reporters that he believes Colbern has no connection to the plot.

Officials said last week that John Doe No. 2, the dark-haired man reportedly seen with McVeigh when he rented a truck in Junction City, Kan., four days before the blast, may not have been actively involved in the plot. He continues to elude the largest dragnet in American history.

A federal official said investigators were still sorting through “the avalanche of leads” from citizens, some of which had steered agents off track.

Agents have been poring through telephone records of some 66,000 calls made by McVeigh and Nichols, as well as several of their associates. And they have scoured fertilizer supply outlets in Kansas and Oklahoma, making copies of sales receipts that date from late 1994 to the present.

Kansas farm supply dealers have told agents the bomb ingrediants could have been purchased for around $1,000 and easily packed into a rental truck by two men.

Some militia leaders in Kansas and Michigan have cooperated with authorities, providing information on members linked to radical farm protest groups such as Posse Comitatus, We the People or the Common Law Courts movement, which have advocated violence against federal officials.

In letters sent to local officials since 1992, Nichols declared himself a “sovereign citizen” who is not bound by federal law, using language that mirrors the doctrines of these agrarian revolt groups.

Marife Nichols, the mail-order bride Nichols married in the central Philippines town of Cebu on Nov. 20, 1990, returned to her homeland last week after being released from federal custody. She was questioned by authorities for 34 days but reportedly was not brought before the grand jury.

McVeigh’s attorney Stephen Jones began his own investigation by traveling to Waco, Texas, to view the remnants of the Branch Davidian compound and then to Junction City.

Jones refused to discuss his findings.

In a setback to the prosecution, Terry Nichols’ brother, Michigan farmer James Nichols, who was charged first with being a material witness to the blast and then with unrelated explosives violations, was released last month to the custody of his neighbors after a federal judge ruled that no hard evidence linked him to the bombing.

In contrast to the depiction of him as a silent prisoner of war, McVeigh’s attorneys said he has provided them with information.