As police divers continued searching the East River Thursday for the gun used in the killing of an NYPD housing cop, a law enforcement official said investigators believe they have enough evidence to build a case against murder suspect Tyrone Howard without the weapon.

Police suspect Howard, 30, tossed a .40 caliber handgun into the East River after allegedly using it to shoot Officer Randolph Holder, 33. The ex-con is charged with one count of first degree murder.

Meanwhile, Howard remained locked away in a jail cell Thursday and NYPD officials changed the location of Holder's wake and funeral because of the large contingent of police expected. Other officers spent part of the day paying tribute to their fallen comrade at Ground Zero.

Critical evidence already in the hands of detectives includes an eyewitness account of the shooting from Holder's partner, Officer Omar Wallace.

Police said after Howard shot Holder, Wallace returned fire. A bullet struck Howard in the leg, officials said. In addition, cops have a description identifying the suspect from the man whose bike they said Howard took at gunpoint about 8:41 p.m. Tuesday night near 104th Street and the FDR Promenade. Howard robbed the man after fleeing from an earlier shooting near the East River Houses, police said.

Other witnesses told investigators they saw Howard throw an object police later retrieved and identified as a clip from a .40-caliber handgun.

A law enforcement source who didn't want to be named said one gap in the physical evidence is the missing bullet that passed through Randolph's skull. Even if divers find the weapon, without the spent bullet they would have nothing to test for ballistic analysis. The city medical examiner's office didn't return a request for information about the autopsy findings on Holder's death.

Howard also faces a first-degree robbery charge for the bicycle theft. He did not enter a plea late Wednesday night during a contentious arraignment in a Manhattan criminal courtroom packed with NYPD officers and the slain lawman's relatives. Howard's court-appointed defense attorney, Brian Kennedy, didn't return calls for comment Thursday.

Officials changed the location of Holder's wake and funeral from the relatively small Community Church of the Nazarene in Far Rockaway to a larger church because as many as 30,000 law enforcement officers are expected to attend. A visitation is scheduled from 9 a.m. to 6 p.m. Tuesday at Greater Allen A.M.E. Cathedral of New York at 110-31 Merrick Blvd. in Jamaica. A funeral service is set for 3 p.m. Wednesday at the church. Holder, who was not married and lived in Brooklyn, will be buried in a family plot at a cemetery in his native Georgetown, Guyana.

JetBlue has offered complimentary flights to officers who want to attend the services.

The anticipated large police presence is expected to be close to the showing of solidarity seen for the funerals of slain detectives Rafael Ramos and Wenjian Liu after they were shot to death in the Bedford-Stuyvesant section of Brooklyn last December.

Holder's funeral is being arranged with the assistance of the NYPD ceremonial unit under the command of Lt. Tony Giorgio. Ceremonial unit cops will act as pallbearers while members of Holder's unit, Police Service Area 5, will serve as honor guard.

At the World Trade Center, police officers and others remembered Holder Thursday with a moment of silence. They laid flowers at the Sept. 11 memorial's south reflecting pool.

A similar ceremony was held for Liu and Ramos last year.

"It's a sad occasion but important to remind the world that police officers are getting up everyday to put their lives on the line and this is a place for the city and the country to do just that," said Joe Daniels, president and chief executive of the National September 11 Memorial & Museum. Daniels said the Sept. 11 memorial south reflecting pool "is a place to recognize the sacrifice of all responders . . . to have these murders happen is unacceptable."

With Maria Alvarez