WASHINGTON "” Investigators from Scotland Yard have concluded that Benazir Bhutto, the Pakistani opposition leader, died after hitting her head as she was tossed by the force of a suicide blast, not from an assassin's bullet, officials who have been briefed on the inquiry said Thursday.

The findings support the Pakistani government's explanation of Ms. Bhutto's death in December, an account that had been greeted with disbelief by Ms. Bhutto's supporters, other Pakistanis and medical experts.

Also on Thursday, the Pakistani government announced the arrest of two more suspects in connection with the assassination plot but gave few other details.

Thousands of Ms. Bhutto's supporters gathered in her hometown in southern Pakistan, marking the end of a 40-day mourning period.

It is unclear how the Scotland Yard investigators reached such conclusive findings absent autopsy results or other potentially important evidence that was washed away by cleanup crews in the immediate aftermath of the blast, which also killed more than 20 other people.

The British inquiry also determined that a lone gunman, whose image was captured in numerous photographs at the scene, also caused the explosion, said the officials, who spoke on condition of anonymity because the report has not been made public. Pakistani authorities originally said there were two assailants, based partly on photographs splashed across the front pages of the nation's leading newspapers.

Scotland Yard investigators relayed their key findings to the government of President Pervez Musharraf on Thursday, according to the officials.

The investigators are expected to present a formal report to the Pakistani government on Friday, as well as to Ms. Bhutto's widower, Asif Ali Zardari, now co-chairman of her Pakistan Peoples Party, and the couple's 19-year-old son, Bilawal Bhutto Zardari, who is a student in London.

Scotland Yard said through a spokesman in London that it would have no comment on the Bhutto report until after it was made public. The British team is to present its report on Friday to the additional inspector general of police, Abdul Majid, who is leading the Pakistani investigation team.

Scotland Yard's report will be presented just days before the country's parliamentary elections on Feb. 18.

The findings are certain to be met with widespread skepticism, especially from Mrs. Bhutto's supporters who blame the government for her death, in particular Mr. Musharraf and the leading politician of the party that backs him, Pervez Elahi. They also are unlikely to calm the turmoil in the country now that the 40 days of mourning has ended.

Mr. Zardari and his party's supporters say they believe she was shot, as do people who were riding with Ms. Bhutto when she died on Dec. 27 after her vehicle came under attack as she left a political rally in Rawalpindi.

The doctors who treated Ms. Bhutto told a member of the hospital board, an eminent lawyer, Athar Minallah, that she had most likely been shot. Ms. Bhutto's brazen killing set off days of violent protests and rioting across Pakistan. To allay public anger and to lend credibility to the investigations into the assassination plot, Mr. Musharraf invited a team of Scotland Yard forensic experts to assist Pakistani investigators in early January.

But the British investigators have faced several hurdles, including the compromise of the crime scene by cleanup crews and Mr. Zardari's refusal to allow an examination of Ms. Bhutto's body.

Mr. Musharraf has said that among the pieces of evidence potentially available to investigators was an X-ray taken by hospital technicians of Ms. Bhutto's wounded skull. Investigators pored over hundreds of photographs taken at the scene, many by people with cellphone cameras.

The question of an autopsy became central to the circumstances of Ms. Bhutto's death because of conflicting versions of the critical events put forward by the Pakistani government.

Ms. Bhutto was standing in an open-roofed vehicle at the time of the attack. On the night she was killed, an unidentified Interior Ministry spokesman was quoted by the official Pakistani news agency as saying that she had died of a "bullet wound in the neck by a suicide bomber."

But the official account later released by Pakistan's government said that she had not been shot, but had instead died as a result of a skull fracture caused when her head struck a lever on her vehicle's sunroof as she ducked back into the vehicle during the attacks.

Even as the authorities in Islamabad prepared to receive the report, the government on Thursday announced the arrests of the two additional suspects in Ms. Bhutto's death. Pakistani officials said that they were arrested Thursday morning in Rawalpindi, a city about seven miles from the capital that is home to the army's headquarters. They gave few other details.

"All I can say is that two persons by the name of Husnain and Rafaqat were arrested today in the morning," said Javed Iqbal Cheema, a retired brigadier who is the spokesman for the Interior Ministry, in a telephone interview Thursday evening.

The government officials described the arrests as an "important breakthrough," but they did not say what role they believed the two arrested played in Ms. Bhutto's death.

Mr. Cheema denied reports that one of the arrested men was the brother of the man said to have been the suicide bomber. Pakistani officials consider Baitullah Mehsud, the militant leader of the South Waziristan region, as one of the prime suspects in the Bhutto case.

Last month, the authorities arrested a teenager from North-West Frontier Province in connection with the case and later made an additional arrest. Both suspects are now under investigation, according to the Interior Ministry.

In Garhi Khuda Baksh in southern Sindh Province, where Ms. Bhutto is buried at her family mausoleum, caravans of supporters started gathering Thursday morning, according to the local news media. Prayer services were also held in other cities.