Raymond A. Davis, the U.S. official from Highlands Ranch at the heart of a tense stand-off with the Pakistan government, was an ex-Blackwater security employee working for the CIA as an independent contractor when he shot and killed two Pakistani men, according two senior U.S. intelligence officials.In the fullest account yet of how an American official came to be held for the deadly shooting in Pakistan, three current officials told ABC News who Davis was working for and what he was doing on January 27th when the incident occurred.A current senior U.S. official and a senior intelligence consultant who worked with Davis told ABC News that the 36-year-old American had been an employee of the company once known as Blackwater, now called Xe Services, and contracted to the CIA. He was posted to Lahore as part of the CIA's Global Response Staff, or GRS, a unit of security and bodyguards assigned to war zones and troubled countries such as Afghanistan and Pakistan. Members of the GRS most often accompany CIA case officers, who meet with clandestine sources.Davis first arrived in Pakistan in December 2008, and was posted at various times in Islamabad, Lahore and Peshawar, a senior US official told ABC News. Until last August, Davis was stationed in Pakistan as an employee of Xe Services, and contracted to the CIA.A former Blackwater executive told ABC News that the CIA terminated the company's GRS contract in Pakistan, accusing the security company of failing to provide adequate services. The agency then moved to hire Davis and other the former Xe/Blackwater security personnel directly as independent contractors.Davis and a group of fellow security officers lived in a safehouse in Lahore. The CIA keeps safehouses for security personnel in an effort to limit the ability for militants to track their movements, the intelligence contractor said, ABC News reported.On Jan. 27, Davis left the safehouse and conducted an "area familiarization route," the senior U.S. official told ABC News. He drove through various Lahore neighborhoods for several hours. It was during his route, two U.S. officials say, that Davis stopped at an A.T.M. and possibly drew the attention of two Pakistani men on a motorcycle.Davis has told the police in Lahore that the two men were attempting to rob him when he fired several rounds from his Glock handgun hitting them both. Davis fired multiple rounds from inside his car, killing one man in the street, while the second died later from his injuries.Davis then called for help from several other CIA security officers who shared his Lahore safehouse, the U.S. official and the intelligence consultant told ABC News. As they arrived near the intersection, they accidentally hit a Pakistani bicyclist, the two officials said. The bicyclist later died of his injuries. Davis' colleagues were unable to get to Davis before the police arrested him. They left the scene and returned to their safehouse. Within hours, they had destroyed all government documents at the safehouse, abandoned it, and retreated to the US consulate for safety, ABC News reported. Both have since returned to the US, according to a senior U.S. official briefed on the case.Davis has been held ever since by the local police. Pakistani authorities have said Davis is now in the legal system, which will soon determine if he should stand trial for murder, different crimes, or release him.The Pakistani government is under significant public pressure to prosecute Davis. The incident has set off massive anti-American protests and calls for Davis to be executed for the murders."Our first fear is that the sentiment of the street in Pakistan is, 'Let's take him and hang him,'" a current senior U.S. official told ABC News.According to the official, administration officials fear that the Pakistani government lacks sufficient control over Pakistani municipal police, who have Davis in custody.U.S. officials have been in a standoff with the Pakistani government over Davis's detention since his arrest. The U.S. asserts that Davis has diplomatic immunity and is protected under the Vienna Convention, which recognizes diplomatic immunity. Pakistani officials have denied that his diplomatic passport protects him from the country's judicial system."His continued detention is a gross violation of international law," the U.S. Embassy in Islamabad, Pakistan, said in a statement last week. "Under the Vienna Convention and Pakistani domestic law, he is entitled to full criminal immunity and cannot be lawfully arrested or detained."In recent days the Obama administration has summoned the Pakistani ambassador to the White House to demand Davis's release, while Secretary of State Clinton and the US ambassador to Pakistani and asked senior Pakistani military, intelligence and other government officials to respect Davis's diplomatic immunity.But the U.S. has refused to elaborate publicly on Davis' position in Pakistan except to say he was a "technical advisor" for the consulate in Lahore and to refer to him as a "diplomat" in public statements.As a GRS officer, Davis made $780 per day working as a security guard for the agency's clandestine case officers, ABC News reported. One official described his job as always being "a few tables away" from a case officer meeting with a clandestine source, and providing security escorts around the country. By 2010, Davis had been moved to Peshawar.In recent years the Pakistani media has asserted that Blackwater was responsible for numerous terrorist attacks in the restive western areas of the country -- attacks attributed by the Pakistani and American governments to the Taliban, al Qaeda and other militant Islamic groups, ABC News reported.The intelligence consultant told ABC News that Blackwater personnel have worked for the CIA in Pakistan since at least 2004, most as security guards, but some as paramilitary operatives working to target militants in the country's tribal regions.The Pakistani men Davis shot on Jan. 27 were carrying pistols and stolen cell phones, according to the Lahore police. Pakistani government officials have told ABC News that the two were working for that country's intelligence agency, Inter-Service Intelligence, and were also conducting surveillance. American officials deny that the two men worked for the ISI."We have no information to suggest Davis was being followed by the ISI," one current U.S. official told ABC News.