In an effort to tamp down the furor in Pakistan over the case, Mr. Kerry, the chairman of the Senate Foreign Relations Committee, spoke in conciliatory terms yet stressed the principle of diplomatic immunity after landing in Lahore, the city where the official, Raymond A. Davis, is accused of shooting two Pakistani motorcyclists who he has said tried to rob him.
The episode three weeks ago has aroused a tide of anti-American emotion that threatens the survival of the pro-American Pakistani civilian government, and it has greatly damaged the already tense relations between the United States and Pakistan, a downturn Mr. Kerry said he hoped to reverse.
“Our Department of Justice will conduct a criminal investigation,” Mr. Kerry told a group of Pakistani television anchors, an assurance that Washington had not offered so far. “That doesn’t mean the law of immunity is not to be respected.”
At a news conference in Washington, President Obama stressed that Pakistan must abide by the conventions of diplomatic immunity and that Mr. Davis, a former Special Forces soldier who was assigned to the American Embassy in Islamabad as a “technical and administrative” official, was not subject to prosecution by the Pakistani courts.
The government of President Asif Ali Zardari has declined to grant diplomatic immunity to Mr. Davis.
The Pakistani press has questioned whether Mr. Davis is a diplomat and criticized what is being termed arrogance by the United States in allowing an official to drive with a loaded Glock pistol, 75 9-millimeter bullets and five magazines on a crowded downtown street. An hour before Mr. Kerry arrived, one of the most popular television hosts, Kamran Khan, said that granting immunity to Mr. Davis meant countries could send “anyone anywhere to kill.”
A high court in Lahore is scheduled to hear an opinion by the Pakistani foreign office on Thursday on the question of immunity for Mr. Davis.
The former foreign minister, Shah Mehmood Qureshi, who lost his job in a cabinet reshuffle on Friday, said he had refused a request by Secretary of State Hillary Rodham Clinton to certify diplomatic immunity for Mr. Davis because the “official record” of the foreign office did not warrant it. Mr. Qureshi was widely interpreted by politicians here as following the wishes of the military, which is essentially in charge of Pakistan’s foreign policy.
On Tuesday morning, the Lahore police submitted a report of its investigation to the court refuting Mr. Davis’s claim of self-defense.
It stated that Mr. Davis fired at the men from inside the car he was driving and then fired at them after stepping out of the car.
The report said that Mr. Davis had shot the men in the back, as well as in the front, firing 10 bullets in all. One man was shot while running, the report said.
At the time of the shooting, Mr. Davis, 36, was driving alone on a busy thoroughfare in Lahore when two men, according to the police, tried to rob him.
According to the police report filed Tuesday, the two men carried pistols, that were not loaded.
After Mr. Davis shot the men, he photographed their bodies and called for help on his cellphone. An S.U.V. from the American Consulate in Lahore rushed to the scene and knocked over a motorcyclist who later died. That vehicle fled the scene, and the Lahore police have demanded that the Americans in that car report to the authorities.
The police investigation said that the S.U.V. carried a fake license plate. Some gear fell from that vehicle as it sped away, including 100 bullets, four battery cells and a piece of cloth with an American flag stamped on it, the report said.
In Mr. Davis’s car, the gear included the Glock pistol and ammunition, a variety of flashlights, a long wrench and a small packet of what is known as naswar, a mild narcotic commonly used in the tribal areas of northwest Pakistan adjacent to Afghanistan, the police report said.
After more than 10 days of detention at a police training center, Mr. Davis was moved to the central prison in Lahore last week, where he slept on a foam pad on a concrete floor, according to a statement by the American Consulate in Lahore.
The government of President Zardari has been troubled by threats from religious groups, emboldened by the recent shooting of a secular politician by his own bodyguard, of mayhem on the streets if Mr. Davis is sent back to the United States.
The government’s position has been complicated by the fact that Mr. Davis is being held in the jurisdiction of Punjab Province, where right-wing religious fervor is gaining strength and where former Prime Minister Nawaz Sharif wields political power.
On Wednesday, Mr. Kerry is scheduled to meet Mr. Sharif in Islamabad, American officials said Mr. Kerry would impress upon Mr. Sharif that Mr. Davis’s case should be decided in the United States, they said.
Mr. Kerry, who is well known in Pakistan as the sponsor of a five-year $7.5 billion aid package, was also expected to meet with Mr. Zardari and the army chief, Gen. Ashfaq Parvez Kayani, they said.