"Exotic" batteries ordered online helped lead authorities to the Austin, Texas, bombing suspect before he died early Wednesday as police closed in, multiple senior law enforcement officials told NBC News.
Austin police and federal agents had been working around the clock with 350 agents to track down the 24-year-old bombing suspect.
Police did not name the bomber, but two law enforcement sources familiar with the investigation identified him to NBC News as Mark Anthony Conditt.
The unusual batteries used in the explosives were the signature trait that allowed investigators to so quickly link the various explosions to the same man, sources said. One senior law enforcement official said the batteries came from Asia.
"These weren't your store-bought Duracells," one official said.
More on this story
Conditt, the suspect in a spate of bombings that terrorized Austin, died early Wednesday after detonating an explosive inside his vehicle as a SWAT team tried to apprehend him on the side of a highway, officials said.
Authorities had tracked him to a hotel in Round Rock, a city in the Austin metropolitan area, Austin Police Chief Brian Manley said at a news conference.
Police were able to locate Conditt using a variety of tactics, including coming up with a list of phone numbers and individuals that were in the area of the bombings when they occurred, using cell-site analysis and high-tech computing systems that can find patterns of callers in certain areas.
Hours before police attempted to pull Conditt, he turned on his cell phone, which allowed authorities to track his location.
Surveillance footage taken at an Austin FedEx was also used to apprehend him.
Authorities shared the surveillance footage showing a man believed to be Conditt entering a FedEx facility wearing what appeared to be a blonde wig and dropping off a package.
Early Wednesday, police tracked Conditt's vehicle until he pulled over on Interstate 35 and "the suspect detonated a bomb inside the vehicle, knocking one of our SWAT officers back," Manley said, adding that the officer sustained minor injuries.
Another member of the SWAT team fired and, as is standard practice, has been placed on administrative duty while the investigation continues, Manley said.
"The suspect is deceased and has significant injuries from a blast that occurred from detonating a bomb inside his vehicle," he added.
A 2012 blog, which appears to be part of a government class project at Austin Community College, lists the author as Mark Conditt of Pflugerville, Texas. Conditt is believed to have been a resident of Pflugerville, north of Austin.
NBC News could not immediately confirm if the blog belonged to the suspect, but public records show only one Mark Conditt in Pflugerville. Austin Community College confirmed that a "Mark Anthony Conditt" born in June 1994 was a student from 2010-2012, but did not graduate, adding that the school is "working with Austin Police Department to provide any information they need."
The blog espouses political beliefs, including entries describing why the author believes gay marriage should not be legalized and why the United States should do away with sex offender registration.
"I am not that politically inclined. I view myself as a conservative, but I don't think I have enough information to defend my stance as well as it should be defended," a description of the author reads. "The reasons I am taking this class is because I want to understand the US government, and I hope that it will help me clarify my stance, and then defend it."
Jeff Reeb, a neighbor of the Conditt family, said the 24-year-old was "a very normal kid" and that the family is "extremely nice."
"I can't imagine what any of them are going through ... just really nice, calm family if you can say it that way," Reeb said.
Shortly after the announcement that the suspect had been killed, President Donald Trump congratulated law enforcement personnel.
Austin Mayor Steve Adler echoed the praise on "Today": "As a community, we're just really relieved and just incredibly thankful for this army of law enforcement that has been in our community for the last week or so."
The police, FBI, and personnel with the Bureau of Alcohol, Tobacco, Firearms and Explosives were deployed to the scene, the ATF said in a tweet earlier in the morning.
The incident happened at around 2 a.m. local time (3 a.m. ET), according to NBC affiliate KXAN.
Even though the suspect is dead, officials warned locals to keep on the lookout for other possible explosives.
"This is the culmination of three very long weeks for our community," Manley said. "We don't know where the suspect has spent his last 24 hours, and therefore we still need to remain vigilant to ensure no other packages or devices have been left in the community."
ATF Special Agent in Charge Fred Milanowski told reporters that officials were "concerned that there may still be other devices out there."
Austin has been on edge after a series of package or other bombs detonated across the city over the past few weeks.
The most recent occurred Sunday when two people were injured by a device believed to have used a tripwire.
Authorities have warned that the devices appeared to be getting more sophisticated and asked residents of one neighborhood to stay indoors Monday.
The FBI has sent 350 special agents to the Texas capital as well as extra bomb squads.
"We are clearly dealing with a serial bomber," Manley said Monday. "We will have to determine if we see a specific ideology behind this."