Three of Dzhokhar Tsarnaev's college classmates have apparently been arrested by federal authorities for aiding Tsarnaev after the bombings — and according to one veteran criminal defense lawyer, this is a common development.

Ron Kuby has been practicing law in New York City for 30 years, logging enough experience with similar cases that he's earned a spot on the "terror bar," in his own estimation. We spoke with him Wednesday afternoon in an effort to learn how arrests like this happen — and how roommates of alleged criminals might be implicated.

(Update: Original reports suggested that the new suspects were roommates of Tsarnaev; that appears not to be the case. Our questions to Kuby assumed they were.)

"These types of charges after the fact are not unusual," Kuby told us. He pointed to the case of Najibullah Zazi, arrested in 2010 as part of a plot to attack subways in New York City. According to Kuby's, Zazi's family "in an incredibly misguided attempt to help their loved one" destroyed evidence central to the case. Eventually, Zazi pled guilty in part to protect his mother from having charges filed against her.

Kuby suggests there is another common response: self-protection. He calls this the "clean house syndrome," the impulse to get rid of any evidence at hand. "It would be disheartening but not unusual for young people who suddenly find that their roommate and friend is a terrorist and a murderer to get rid of everything," Kuby said, "so they don't implicate themselves." And then, it would be common to lie about it. The response from authorities would differ, depending on what the root charges were. "In another type of case" — like possession of marijuana — such behavior "would be overlooked." For Tsarnaev's roommates, at least two of whom were apparently in the country on student visas, their proximity to Tsarnaev already put them in a perilous position. Panic would not be unexpected.

But for charges to stick, the roommates will have had to have done something. Early reports that they threw away a backpack owned by Tsarnaev qualifies. If they had simply known about the terror attack after the fact, it would not. "No one has an affirmative obligation to turn people into the authorities," said Kuby. "You do have an affirmative obligation to not conceal evidence. You have an obligation not to lie to federal officials." According to reports on CNN, the filed charges include obstruction of justice — and lying to authorities. If the roommates were informed of Tsarnaev's role and didn't initially tell authorities, it could prompt authorities to take "a much harsher view" of any action they did take.

"Based on the very little I've heard," Kuby summarized, "it sounds like these kids panicked after the fact, and engaged in ill-advised and arguably criminal things." Whether or not they acted at the behest of Dzhokar may not have mattered much to authorities. It could be far more significant if and when the case comes before a jury.

Update, 2:19 p.m.: The criminal complaint against the accused appears to suggest that Kuby's assumption was largely correct. One excerpt: