Police planned to release more information Thursday afternoon about two possible suspects in the Boston Marathon Bombing in an attempt to yield public information that could lead to an arrest.
Footage from a surveillance camera has led investigators to believe two separate suspects planted a black bag at each of the explosion sites near the marathon finish line. But uncovering their identity is only half of equation.
Determining the motivation of the bombers is a critical part of developing some sort of conclusion to what could be the first foreign attack on U.S. soil since Sept. 11, 2001. And one retired senior Pentagon intelligence official points to a potential overseas connection.
"This looks like an Afghan-style operation, and most Afghan training comes from ISI," the former intel official said via email, referencing Pakistan's Inter-Services Intelligence agency.
"The way it was placed and went off is indicative of the way ISI plants bombs," says the former official, who requested anonymity.
The attack in Boston was "very sophisticated," the official adds, despite the rudimentary materials used for the pressure cooker bomb.
The Pakistani Taliban has said it believes in attacking the U.S. and its allies but denied involvement in the Boston bombing, a spokesman tells AFP.
A Marine Corps commander fresh back from the front lines in Afghanistan says the threat of an IED attack should have always been a concern on U.S. soil.
"It shouldn't be a surprise," said Maj. Gen. Charles Gurganus, commander of the I Marine Expeditionary Force. "It's a bomb, and you can figure out how to make that if you just look on the internet."
"I don't draw the conclusion that now we need to start worrying about this," he said at a breakfast meeting with defense reporters in Washington on Thursday. "I think we always should have been, and it's going to be a growing concern still."
Some of the best money the U.S. military has spent in training its soldiers is through the Joint Improvised Explosive Device Defeat Organization, Gurganus says, "but we haven't solved the problem."
IMEF was deployed to Helmand and Nimroz provinces in Southern Afghanistan as the primary force for Regional Command-Southwest.
While Pakistan and the U.S. maintain a very close economic and strategic relationship - with the U.S offering tens of millions of dollars each year in aid - the U.S. remains wary of its intelligence service, and Pakistan has lambasted the U.S. for drone strikes on its own soil.
The American government kept Pakistan and ISI in the dark about the 2011 raid that killed al-Qaida leader Osama bin Laden for fear the information would leak.
"There is a lot of factionalization within the ISI and people who have extremely bad feelings about the U.S.," says the retired Pentagon official who spoke with U.S. News. "It could be reprisals; payback for coming into our neighborhood."
Any evidence that this could be true would create a sticky situation for the U.S., he says, unlike with Iran, for example, where the Iranian Republican Guard has already been classified as a terrorist group, making it straight-forward to launch a counter strike.
One expert in the weaponry used in America's modern wars in Iraq and Afghanistan says the attention given to IEDs from all sides of the fight could muddy the issue.
"Inspire magazine is well publicized by the press," says Bill Roggio, a reporter for The Long War Journal, of the al-Qaida publication that instructs readers on how to perform homegrown terrorism. "This is what [al-Qaida] advises to do: Build a bomb like this."
Pressure cooker bombs have long been used in attacks linked to jihadist groups, but also among U.S. bombers - Army Pfc. Naser Jason Abdo assigned to Fort Hood was arrested in 2011 for buying the ingredients to build such a bomb in Killeen, Texas.
Al-Qaida in the Arabian Peninsula has developed a manual on building this kind of bomb, which the FBI publicized in a bulletin warning of its proliferation and danger.
All of this public information makes it easier for copycats to get the training and resources they need to carry out an attack.
All that can be inferred so far is that the bomber knew what he was doing.
"If you're smart enough to pull off an attack like this, you're probably smart enough to cover your tracks," says Roggio.
But another former investigator cautions officials should keep an open mind on how the Boston bombing was planned and executed.
"It's important not to have a preconceived mindset," says Fred Burton, a former Diplomatic Security service who worked the 1993 World Trade Center bombing and 1996 Atlanta Olympics. "Every time we identify what we think is the leading suspect, it turns out to be a 180-degree difference."
Early on, federal agencies such as the FBI believed the Oklahoma City bombing was the work of Hezbollah, he says, but it turned out to be Timothy McVeigh.
"It's very important to take into account when you look at the forensics with this kind of IED, that the range of potential actors that could have put this together really spans the spectrum," Burton says. Separate people or groups may be responsible for paying for the bombs ingredients, for building it and for placing it near the marathon finish line, he says.
"These kinds of devices, they've been around forever going back even to Vietnam," he says. "That's a whole range of different kinds of skill sets, and actors that could have put this together."