John Allen Muhammad, originally named John Allen Williams, was born in Baton Rouge, Louisiana, to Ernest and Eva Williams. The family relocated to New Orleans when his mother was diagnosed with breast cancer, and she passed away when John was just three years old. Shortly after her death, his father left, leading to John being raised primarily by his maternal grandfather and an aunt.

At the age of 26, in 1987, Williams joined the Nation of Islam and later participated in providing security for the "Million Man March" in 1995. However, Nation of Islam leader Louis Farrakhan publicly disassociated himself and the organization from the D.C. sniper attacks. In 1999, Williams abducted his children and fled to Antigua, where he engaged in credit card and immigration document fraud. During this period, he formed a close relationship with Lee Boyd Malvo, a Jamaican youth who would later become his accomplice in the sniper attacks.

In October 2001, Williams legally changed his name to John Allen Muhammad. Following his arrest, authorities reported that Muhammad expressed admiration for Osama bin Laden and al-Qaeda, approving of the September 11 attacks. Malvo testified that Muhammad indoctrinated him to believe that money obtained from their planned extortion would fund a camp in Canada to train homeless children as terrorists.

Muhammad experienced two divorces, with his second ex-wife, Mildred Muhammad, obtaining a restraining order against him due to allegations of abuse. Muhammad was later arrested for violating this restraining order by possessing a firearm, which is prohibited under federal law for individuals with restraining orders, as outlined in the Lautenberg Amendment to the Gun Control Act of 1968.

During the trials, both defense attorneys in Malvo's case and prosecutors in Muhammad's case argued that the primary motive behind the Beltway sniper murders was Muhammad's desire to kill Mildred and regain custody of his children.

In terms of military service, Muhammad enlisted in the Louisiana Army National Guard as a combat engineer in August 1978. He transitioned to the Regular Army on November 6, 1985, where he trained as a mechanic, truck driver, and specialist metalworker. He demonstrated exceptional marksmanship with the M16 rifle, earning the Expert Rifleman's Badge, the highest level of basic rifle marksmanship in the Army.

Muhammad's military career included service with the 15th Engineer Battalion at Fort Lewis beginning in 1985. He participated in the Gulf War in 1991, where his unit dismantled Iraqi chemical warfare rockets, earning him several medals, including the Southwest Asia Service Medal, Kuwait Liberation Medal (Saudi Arabia), and Kuwait Liberation Medal (Kuwait). In 1992, he served at Fort Ord, California, with the 13th Engineers, and returned to Fort Lewis in 1993 with the 14th Engineer Battalion.

After 16 years of service, Muhammad was honorably discharged from the Army on April 26, 1994, with the rank of sergeant. His military awards included the Army Service Ribbon, National Defense Service Medal, Overseas Ribbon, Noncommissioned Officers Professional Development Ribbon, and the Army Achievement Medal.

Police discovered a crucial lead when Muhammad or Malvo left a note at a shooting scene, directing investigators to a robbery-murder at a liquor store in Montgomery, Alabama. At this crime scene, investigators found a magazine with Malvo's fingerprints. Malvo's prints were already in the INS database, and he was known to associate with Muhammad. The two had lived together in Tacoma, Washington, where Malvo used the alias John Lee Malvo.

Authorities identified Muhammad and learned he had purchased a former police car, a blue Chevrolet Caprice, in New Jersey on September 11, 2002. This information was shared with the public, leading to the arrest of Muhammad and Malvo when their vehicle was spotted at an Interstate 70 rest stop in Myersville, Maryland.

On October 24, 2002, Muhammad was captured in Maryland, where most of the shootings and murders took place. Although Maryland wanted to prosecute him, U.S. Attorney General John Ashcroft transferred the case to Paul Ebert, the Commonwealth's Attorney for Prince William County, Virginia, as Virginia was more likely to impose the death penalty. This decision was supported by the verdicts in Virginia and Maryland, as Virginia also allowed the death penalty for juveniles.

In 2003, Malvo and Muhammad were named in a civil lawsuit by the Brady Center to Prevent Gun Violence on behalf of their victims and families. The lawsuit resulted in a $2.5 million settlement from co-defendants Bull's Eye Shooter Supply and Bushmaster Firearms, Inc.

In October 2003, Muhammad was tried for the murder of Dean Meyers in Prince William County, Virginia. The trial was moved to Virginia Beach, about 200 miles away. Muhammad initially represented himself but later opted for legal representation after his opening statement. He faced charges of murder, terrorism, conspiracy, and the illegal use of a firearm, all carrying the possibility of the death penalty.

Prosecutors argued that the shootings were part of a scheme to extort $10 million from local and state governments. They presented evidence of 16 shootings attributed to Muhammad. The terrorism charge required proof of at least two shootings within three years. The prosecution called over 130 witnesses and presented more than 400 pieces of evidence, including a rifle linked by ballistics to eight of the ten Washington-area killings and two others in Louisiana and Alabama. Other evidence included the modified car trunk from which the shootings were carried out and a laptop with maps of the shooting scenes.

Muhammad's defense argued there was no direct evidence linking him to the murders, contending that under Virginia's "trigger-man law," Muhammad could not be sentenced to death unless he was proven to have fired the fatal shot. However, on November 17, 2003, Muhammad was convicted on all counts, including two capital murder charges and conspiracy. The jury recommended the death penalty, and on March 9, 2004, a Virginia judge sentenced Muhammad to death.

The Virginia Supreme Court upheld his death sentence on April 22, 2005, rejecting the defense's argument that Muhammad was not the triggerman. Justice Donald W. Lemons highlighted Muhammad's extensive planning and disregard for life in his ruling.

In 2005, Maryland and Virginia agreed to extradite Muhammad to face charges in Maryland. He was held at Sussex I State Prison in Virginia and later extradited to Montgomery County, Maryland, where he was convicted of six counts of murder and sentenced to six consecutive life terms without parole on June 1, 2006.

During Muhammad's 2006 trial in Maryland, Malvo confessed to a more detailed version of their crimes, revealing Muhammad's plans to recruit young boys for mass shootings across the U.S. He outlined a three-phase plan that included meticulous planning of the shootings, killing a pregnant woman and a police officer, and extorting money from the government. Malvo's testimony was critical in detailing the extent of their plot and Muhammad's role in orchestrating the shootings.

On May 6, 2008, Muhammad requested in a letter that prosecutors help end his legal appeals, calling himself an "innocent black man." His defense lawyers cited evidence of brain damage affecting his competency to make legal decisions.

On September 16, 2009, Judge Mary Grace O'Brien set Muhammad's execution date for November 10, 2009. His final appeal was denied by the U.S. Supreme Court on November 9, 2009. Muhammad was executed by lethal injection on November 10, 2009, at Greensville Correctional Center in Virginia. His body was cremated, and the ashes were given to his son in Louisiana.