Kasi was born on either 10 February 1964 or 1 January 1967 in Quetta, Pakistan. He entered the United States in 1991 under the name Mir Aimal Kansi, taking a substantial sum of cash he had inherited on the death of his father in 1989. He travelled on forged papers he had purchased in Karachi, Pakistan, altering his name to "Kansi", and later bought a fake green card in Miami, Florida.
He stayed with a Kashmiri friend, Zahed Mir, in his Reston, Virginia apartment, and invested in a courier firm, for which he also worked as a driver. This work would be decisive in his choice of target: "I used to pass this area almost every day and knew these two left-turning lanes [were] mostly people who work for CIA."
According to Kasi, he first began to think of attacking CIA personnel after buying a Chinese-made AK-47 from a Chantilly gun store. The plan soon became "more important than any other thing to [him]."
On January 25, 1993, Kasi stopped a borrowed brown Datsun station wagon behind a number of vehicles waiting at a red traffic light on the eastbound side of Route 123, Fairfax County. The vehicles were waiting to make a left turn into the main entrance of CIA headquarters. Kasi emerged from his vehicle with his semi-automatic Type 56 assault rifle and proceeded to move among the lines of vehicles, firing a total of 10 rounds into them, killing Lansing H. Bennett, 66, and Frank Darling, 28. Three others were left with gunshot wounds. Darling was shot first and later received additional gunshot wounds to the head after Kasi shot the other victims.
Kasi climbed back into his vehicle and drove to a nearby park. After 90 minutes of waiting, he realized that he was not being actively sought and so he drove back to his Reston apartment. He hid the rifle in a green plastic bag under a sofa, went to a McDonald's to eat, and booked himself into a Days Inn for the night. The CNN news reports he watched made it clear that police had misidentified his vehicle and did not have his license plate number. The next morning, he took a flight to Quetta, Pakistan. According to Kansi, he killed CIA employees because, "I was real angry with the policy of the U.S. government in the Middle East, particularly toward the Palestinian people," Kansi said in a prison interview with CNN affiliate WTTG.
On February 16, 1993, Kasi, then a fugitive, had been charged in absentia. The charges involved capital murder of Darling, murder of Bennett, and three counts of malicious wounding for the other victims, along with related firearms charges.
In May 1997, an informant walked into the U.S. consulate in Karachi and claimed he could help lead them to Kasi. As proof, he showed a copy of a driver license application made by Kasi under a false name but bearing his photograph. Apparently, the people who had been sheltering Kasi wanted the multimillion-dollar reward offer for his capture. Kasi stated "I want to make it clear (that) the people who tricked me ... were Pushtuns, they were owners of land in the Leghari and Khosa clan areas in Dera Ghazi Khan, but I will never name them."
As Kasi was in the dangerous Durand Line border region, the informant was told to lure Kasi into Pakistan where he could be more easily apprehended. Kasi was tempted with a lucrative business offer—smuggling Russian electronic goods into Pakistan—which brought him to Dera Ghazi Khan, in the Punjab province of Pakistan, where he checked into a room at Shalimar Hotel. At 4 a.m. on the morning of June 15, 1997, an armed team of FBI officers working with the Pakistani ISI, raided Kasi's hotel room. His fingerprints were taken on the scene, confirming his identity. Sources disagree as to where Kasi was taken next—US authorities claim it was a holding facility run by Pakistani authorities, while Pakistani sources claim it was the U.S. embassy in Islamabad—before being flown to the US on June 17 in a C-141 transport. During the flight, Kasi made a full oral and written confession to the FBI.
During the trial, the defense introduced testimony from Dr. Richard Restak, a neurologist and neuropsychiatrist, that Kasi was missing tissue from his frontal lobes, a congenital defect that made it hard for him to judge the consequence of his actions. This testimony was re-iterated by another psychiatrist for the defense based upon independent examination.
Kasi was tried at the Fairfax County Courthouse in Fairfax,Virginia by a jury trial over a period of ten days in November 1997, after he pleaded not guilty to all charges. The jury found him guilty, and recommended punishment for the capital murder charge as death. On February 4, 1998, Kasi was sentenced to death for the capital murder of Darling, who was shot at the beginning of the attack and again after the other victims had been shot. His other sentences of Life imprisonment for the first-degree murder of Bennett, a 60 year sentence for the 3 malicious woundings, and fines totaling $600,000 were rendered moot by his execution.
Kasi was executed by lethal injection on November 14, 2002, at Greensville Correctional Center in Jarratt, Virginia. Kasi's body was repatriated to Pakistan; his funeral was attended by the entire civil hierarchy of Balochistan, the local Pakistan Army Corps Commander and the Pakistani Ambassador to the United States, Ashraf Jahangir Qazi. Mourning his death, the democratically elected ruling provincial party, Mutahida Majlis-i-Amal (MMA) hailed him as "hero of Islam" and Hafiz Hussain Ahmed, an MNA from Quetta declared, "God, destroy those who handed him over to America. God, his murderers, whether in America or in Pakistan, may they meet their fate soon".