Soon after, the brothers encountered police, setting off a furious gun battle in which authorities say they fired handguns and hurled explosives at pursuing officers before Tamerlan Tsarnaev was shot. As the younger brother fled in the vehicle, he apparently ran over Tamerlan, authorities said.
Suspect shopped at fireworks store
More than two months before the marathon bombings, Tamerlan Tsarnaev bought two reloadable mortar style fireworks a New Hampshire store.
On February 6, Tsarnaev had one question for a store assistant at Phantom Fireworks in Seabrook, New Hampshire: "What's the biggest and loudest thing you have?"
After that, store Vice President William Weimer said, Tsarnaev shelled out $200 cash for two "lock and load kits."
Weimer said such behavior is very common in the store. He said the store notified the FBI after discovering that the marathon bombing suspect had bought explosives there.
Law enforcement officials told CNN earlier Tuesday that the number of fireworks bought at the store was not enough to set off explosions the size of those at the Boston Marathon.
"My assumption is they bought this, experimented with it and decided against it and moved on and found another source," Weimer said.
Details emerge about boat, standoff
Tamerlan Tsarnaev was pronounced dead early Friday. On Friday night, police captured Dzhokhar Tsarnaev hiding inside a boat in a backyard.
Boat owner David Henneberry told CNN affiliate WCVB Tuesday that his obsession with how his boat was stored just right led him to discover the suspect as he stood on a ladder replacing two pads that had fallen out of the shrink wrap protecting his boat for the winter.
"I got three steps up the ladder and rolled the shrink wrap. I didn't expect to see anything, but I saw blood on the floor of the boat. A good amount of blood. ... And I looked back and forth a couple of times and my eyes went to the engine block and there was a body," he told the affiliate.
Henneberry said Tuesday that he doesn't even remember climbing down the ladder and running to the phone to dial 911, delivering the tip that would lead to Tsarnaev's capture.
"I didn't waste any time. I didn't ask him if he wanted a cup of coffee. I was off that ladder. That is all I remember," he told the affiliate.
Investigators swarmed the scene, forming a perimeter. Multiple shots rang out from behind the house, Boston Police Superintendent William Evans said Tuesday.
Authorities are still investigating whether Tsarnaev was armed and whether a shootout occurred at the boat, Evans told reporters.
"Clearly from everybody's vantage point, we could see whoever was in that boat was poking at that top," he said.
It wasn't clear at the time, he said, whether the suspect had a handgun or was trying to poke a hole in the boat's cover. After a standoff, hostage negotiators persuaded him to surrender, Evans said.
The Tsarnaev family is from the Russian republic of Chechnya and fled the brutal wars there in the 1990s. The two brothers were born in Kyrgyzstan; Dzhokhar became a U.S. citizen in 2012. His brother was a legal U.S. resident.
Although Tamerlan Tsarnaev had become increasingly radical in the past three or four years, there was no evidence Tuesday of any accomplices or connections to extremists, a U.S. official said.
But Dzhokhar Tsarnaev conveyed to authorities that his brother believed Islam is under attack and its adherents must fight back, a U.S. government source said Monday.
Communicating with investigators by writing and nodding, Dzhokhar Tsarnaev has indicated that his older brother masterminded the bombings, the source said.
The younger Tsarnaev has been charged with using and conspiring to use a weapon of mass destruction resulting in death, as well as one count of malicious destruction of property by means of an explosive device resulting in death.
The U.S. official said Tuesday that investigators have determined that the pressure cookers used in the attacks were purchased at a Macy's department store.