The Boston Marathon bombing: the 33 terabytes, the boat in Watertown, and the 102-hour hunt (2026)

Introduction

The Federal Bureau of Investigation's Boston Marathon Bombing, published in its official case history series, is worth reading for the way it documents how investigators moved from shattered pavement on Boylston Street through 33 terabytes of video evidence to identify two suspects, end a violent four-day manhunt, and build a 30-count federal case. Read the FBI's full case history, which grounds the investigation in physical evidence, public assistance, and respect for the people harmed. 1

Supplementary context on the investigative response, the survivors, and the final judicial rulings is drawn from the FBI Boston Field Office's 10-year anniversary report 2, the Department of Justice sentencing record 3, and the Supreme Court's 2022 opinion in United States v. Tsarnaev 4.

Full summary

On Monday, April 15, 2013, thousands of spectators gathered along Boylston Street in Boston to cheer participants finishing the 117th Boston Marathon. At 2:49 p.m., two improvised pressure-cooker bombs packed with explosive powder, nails, BBs, and scrap metal detonated 11 seconds and roughly 210 yards apart near the finish line. The blasts tore through crowded sidewalks, killing three spectators and injuring more than 500 people, 17 of whom suffered traumatic amputations. 1 2

The victims killed on Boylston Street were Krystle Campbell, a 29-year-old restaurant manager from Medford, Massachusetts; Lingzi Lu, a 23-year-old Boston University graduate student from Shenyang, China; and Martin Richard, an eight-year-old boy from Boston's Dorchester neighborhood whose six-year-old sister Jane lost a leg and whose parents also sustained serious injuries. Bystanders, race volunteers, and emergency personnel immediately converted the finish line into a triage zone, applying makeshift tourniquets from belts and marathon banners that doctors later credited with saving dozens of lives. 2 4

The FBI's Boston Division, led by Special Agent in Charge Richard DesLauriers and working through the multi-agency Joint Terrorism Task Force, assumed lead responsibility for the investigation. Investigators cordoned off a 12-block perimeter along Boylston Street, treating it as one of the largest physical crime scenes in American history. Over the next nine days, approximately 176 personnel from the FBI Laboratory and Evidence Response Teams—working alongside the Boston Police Department, Massachusetts State Police, and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF)—sifted through debris on hands and knees. They recovered shredded black nylon duffel bags, battery fragments, pieces of pressure-cooker lids, circuit boards, and embedded nails, eventually cataloging more than 3,500 pieces of evidence and shipping 2,749 items to the FBI Laboratory in Quantico, Virginia. 1 2

Simultaneously, investigators launched an unprecedented digital triage. The FBI established a specialized digital tip line that collected over 33 terabytes of surveillance video, dashcam recordings, news footage, and spectator cell-phone photographs. Forensic analysts synchronized multiple video angles frame by frame to reconstruct movements along Boylston Street before and after the detonations. The breakthrough occurred when footage from a security camera outside the Forum restaurant revealed a young man in a white baseball cap turned backward standing with a bulky backpack among spectators, remaining calm when the first blast detonated up the street, and walking away seconds before his own abandoned backpack exploded. By tracing his movements in reverse, analysts paired him with a second man in a dark cap and sunglasses who had dropped the first bomb. 1 2

On the afternoon of Thursday, April 18, 2013, the FBI released still photographs and video clips of the two unidentified suspects to the public, asking for assistance in determining their names. The public release immediately altered the trajectory of the case. Within hours, the suspects realized that law enforcement was closing in and mobilized to flee the Boston area. 1 4

Later that night, the two men—identified subsequently as brothers Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev, 19—drove to the Massachusetts Institute of Technology campus in Cambridge. At approximately 10:25 p.m., they ambushed 27-year-old MIT Police Officer Sean Collier as he sat in his patrol cruiser, shooting him five times at point-blank range in an unsuccessful attempt to steal his service handgun. Minutes later, the brothers carjacked a Mercedes SUV and took its owner, graduate student Dun Meng, hostage at gunpoint, robbing him of $800. When the brothers stopped at a Cambridge gas station to purchase snacks and fuel, Meng seized a split-second opportunity to bolt from the passenger seat and run across the street into an open convenience store to call 911. 1 2 3

Meng's escape provided the critical operational lead. He informed responding Cambridge police officers that his vehicle contained an active GPS tracking system and that his cell phone remained inside. Law enforcement tracked the Mercedes signal into neighboring Watertown. At around 12:45 a.m. on April 19, Watertown police officers intercepted the SUV on Laurel Street, initiating a ferocious street gun battle. The Tsarnaevs fired hundreds of rounds from a Ruger nine-millimeter pistol and hurled five homemade explosive devices, including another functional pressure-cooker bomb that exploded in the street. As officers tackled and attempted to handcuff Tamerlan Tsarnaev when his gun ran out of ammunition, Dzhokhar leapt into the stolen Mercedes, accelerated directly at the officers, and ran over his brother while speeding away. Tamerlan died shortly afterward from gunshot wounds and blunt-force trauma. 1 3 4

Dzhokhar abandoned the bullet-riddled SUV several blocks away and fled on foot. Massachusetts authorities issued an unprecedented voluntary shelter-in-place request for the greater Boston metropolitan area, halting public transit and closing businesses while hundreds of officers conducted door-to-door tactical searches. Shortly after the order was lifted on Friday evening, April 19, a Watertown homeowner noticed torn shrink-wrap and bloodstains on a drydocked boat stored in his backyard on Franklin Street. Law enforcement converged on the location. After a tense standoff during which the suspect was wounded, federal and local tactical teams took Dzhokhar Tsarnaev into custody at 8:42 p.m. Inside the boat's cockpit, investigators discovered pencil writings and carvings on the wooden bulkhead in which Tsarnaev justified the attacks and declared his desire for martyrdom. 1 4

In June 2013, a federal grand jury indicted Dzhokhar Tsarnaev on 30 counts, including use of a weapon of mass destruction resulting in death, bombing of a place of public use, and malicious destruction of property. Following a 10-week trial in Boston featuring more than 1,000 exhibits and testimony from over 150 witnesses, a federal jury convicted Tsarnaev on all 30 counts on April 8, 2015. On May 15, 2015, the same jury recommended capital punishment on six counts related to the bomb he planted outside the Forum restaurant. On June 24, 2015, U.S. District Judge George A. O'Toole Jr. formally imposed the death sentence alongside multiple consecutive life prison terms. Following intermediate appellate review that temporarily vacated the capital sentences, the Supreme Court of the United States reversed the appellate decision on March 4, 2022, reinstating the jury's death sentences. 1 3 4

Key details

People and roles

Krystle Campbell, Lingzi Lu, and Martin Richard: The three spectators killed near the Boston Marathon finish line on April 15, 2013. Campbell was a 29-year-old manager; Lu was a 23-year-old Boston University graduate student; Richard was an eight-year-old child whose family suffered multiple severe injuries. 2 4
Sean Collier: A 27-year-old MIT Police patrol officer ambushed and fatally shot in his cruiser by the suspects on April 18, 2013, during their attempt to acquire an additional firearm. 1 3
Dun Meng: The graduate student carjacked in Cambridge who escaped at a gas station and gave police the crucial GPS tracking data needed to find the suspects. 2 4
Tamerlan Tsarnaev: The older brother who placed the first pressure-cooker bomb near the finish line, engaged in the Watertown shootout, and died on April 19 after being struck by the fleeing SUV. 1 3
Dzhokhar Tsarnaev: The younger brother who placed the second bomb outside the Forum restaurant, fled the Watertown shootout, and was captured in a drydocked boat. Convicted on 30 federal counts and sentenced to death. 1 3
Dias Kadyrbayev, Azamat Tazhayakov, and Robel Phillipos: Three college acquaintances convicted of federal offenses for removing Tsarnaev's backpack and laptop from his dormitory room or making false statements to federal agents. 1

Timeline

April 15, 2013 (2:49 p.m.) — Boylston Street, Boston: Two pressure-cooker bombs detonate 11 seconds apart near the marathon finish line, killing three spectators and injuring over 500. 1 2
April 16–17 — Forensic processing: The FBI and partner agencies process 12 square blocks, collect 33 terabytes of digital video, and isolate images of two suspects carrying large backpacks. 1 2
April 18 (5:10 p.m.) — Public disclosure: The FBI holds a press conference releasing photos and surveillance video of the two suspects, appealing for public help. 1
April 18 (10:25 p.m.) — Cambridge, Massachusetts: The suspects fatally shoot MIT Police Officer Sean Collier in his cruiser and carjack Dun Meng's Mercedes SUV. 1 3
April 19 (12:45 a.m.) — Watertown, Massachusetts: Police intercept the SUV via GPS; a gunfight ensues; Tamerlan Tsarnaev is fatally injured; Dzhokhar Tsarnaev flees on foot. 1 4
April 19 (8:42 p.m.) — Watertown standoff ends: Dzhokhar Tsarnaev is discovered in a boat in a residential backyard and taken into federal custody. 1
April 8, 2015 — Federal conviction: A jury in U.S. District Court finds Tsarnaev guilty on all 30 counts in the indictment. 1 3
June 24, 2015 — Formal sentencing: Judge George A. O'Toole Jr. sentences Tsarnaev to death and multiple consecutive life terms. 3
March 4, 2022 — Supreme Court ruling: The Supreme Court of the United States reverses a First Circuit decision and reinstates Tsarnaev's capital sentence. 4

What changed the investigation

Digital video reconstruction: Analysts filtered through 33 terabytes of crowdsourced and commercial footage, identifying the backward white cap and matching the suspects' timeline before and after the detonations. 1 2
Public photo release: Distributing the suspects' clear surveillance images forced the brothers out of hiding and precipitated their attempt to flee. 1 4
The hostage's escape and GPS data: Dun Meng's flight at the Cambridge gas station enabled police to immediately track the stolen Mercedes SUV directly into Watertown. 2 4
Physical forensics and Quantico matching: Laboratory analysis established that empty pyrotechnic tubes recovered from Tsarnaev's university dorm room, pressure-cooker parts found on Boylston Street, and unexploded devices in Watertown contained matching explosive compounds and electronic components. 1 3
The boat bulkhead writings: Inscriptions made by Tsarnaev in pencil inside the Watertown boat provided direct evidence of premeditation and ideological motive. 1 4

The legal outcome

A federal grand jury returned a 30-count indictment against Dzhokhar Tsarnaev. On April 8, 2015, following a comprehensive trial presenting over 1,000 physical exhibits, ballistics evidence, and testimony from dozens of victims and experts, a jury convicted Tsarnaev on every count. On May 15, 2015, the jury unanimously recommended the death penalty for six capital offenses related to the bomb he placed in front of the Forum restaurant. 1 3

Judge George A. O'Toole Jr. imposed the death sentence on June 24, 2015, along with multiple consecutive life sentences for non-capital offenses. In July 2020, the U.S. Court of Appeals for the First Circuit vacated the death sentence on procedural grounds related to jury selection and excluded mitigating evidence. The federal government appealed, and on March 4, 2022, the Supreme Court of the United States ruled 6–3 in United States v. Tsarnaev that the district court had acted within its discretion, reversing the First Circuit and reinstating the capital sentence. 3 4

Verbatim quotes

"It was important, first and foremost, to honor the victims." — Joseph Bonavolonta, special agent in charge, FBI Boston Field Division. 2

"Over the next several years, it was the victim's families and the hundreds of survivors who gave us motivation each day to keep pushing forward to get the job done." — Tim Brown, lead case special agent, FBI Boston Field Division. 2

"That’s the first moment I feel like I’m safe. That’s probably a moment I’ll never forget. I really appreciate the officers. They saved my life." — Dun Meng, carjacking survivor. 2

"Dzhokhar Tsarnaev committed heinous crimes. The Sixth Amendment nonetheless guaranteed him a fair trial before an impartial jury. He received one." — Justice Clarence Thomas, writing for the Court in United States v. Tsarnaev, 595 U.S. 302 (2022). 4

References

1
Boston Marathon Bombing
fbi.gov
2
Boston Marathon Bombing Anniversary
fbi.gov
3
Judge Imposes Death Sentence for Boston Marathon Bomber
justice.gov
4
United States v. Tsarnaev
supremecourt.gov