Why the Boston bomber pleaded not guilty even though his lawyer told the court he did it

A jury is now deliberating over whether 21-year-old Dzhokhar Tsarnaev is guilty of bombing the Boston Marathon and killing a police officer in 2013, but his lawyer already admitted at the start of the trial that he did it.

This might seem like a counterintuitive move considering that Tsarnaev pleaded not guilty two years ago when he was charged with planting two bombs near the race's finish line.

But the not guilty plea was likely part of a larger strategy on the part of Judy Clarke, Tsarnaev's attorney who is one of the top death-penalty lawyers in the US. She is aiming to get her client a more lenient sentence and help him avoid the death penalty.

This strategy worked when Clarke defended Jared Lee Loughner, the gunman who in 2011 shot nearly 20 people at a Tucson, Arizona, supermarket, including then-Rep. Gabrielle Giffords. After initially pleading not guilty, Loughner agreed to a deal that took the death penalty off the table.

Legal expert and Ohio State University law professor Douglas Berman told Business Insider last month that the defense could be using the trial as a sort of test run to prepare for the penalty phase, which will decide whether Tsarnaev gets the death penalty.

Tsarnaev's not guilty plea isn't necessarily a claim of innocence but rather an expression that the defense wanted to hold the government to its burden of proof in the case, Berman said. The defense wanted to see how the government was going to put its case together, Berman said.

"The best way to do this is to have this trial phase where the government is going to put forward all of its evidence, which is not just about guilt but why the death penalty is appropriate," he added, "and then the defense has essentially a preview and can then start from the get-go on developing a corresponding, much more informed strategy for the penalty phase."

By entering a not guilty plea and going through a trial, the defense got a look at how the prosecution built its case against Tsarnaev.

"In so many ways, it's not just what's forced the government to show their hand, it's also, 'Let's make our point before the main event and see how the jury seems to be responding and what kind of reactions we think we're getting from the judge and the jury as we put forward a variety of suggestions," Berman said.

Clarke's admission that her client did participate in the bombing could also be a strategic move, which let her build credibility with the jury and make them feel like they could trust her.

Because there isn't much of a question of whether Dzhokhar helped carry out the plot, the defense has focused on diminishing his role and emphasizing the part played by his late older brother, Tamerlan.

On the first day of the trial, Clarke held up two photos of the brothers - one from years before the marathon attack and the second from the scene of the bombing where they're shown carrying backpacks containing explosives, according to the AP. She then asked the jury: "What took Dzhokhar Tsarnaev from this ... to this?"

There is also still potential for Tsarnaev to seek a plea deal down the line, as Loughner did.

"Maybe it's a hope on the part of the defense that if they go through the guilt phase, the government will see that they'll have a challenge getting a death sentence," Berman said. "Given that there's no doubt about guilt and a life sentence is pretty likely regardless, I'm sure the defense is at every stage saying [to the prosecution], either directly or indirectly, 'Is this really worth all your time and energy?'"

Dzhokhar has been charged with planting two bombs near the finish line of the Boston Marathon in 2013. The attack killed three people and injured more than 200 others. His older brother, Tamerlan, whom the defense appears to be portraying as the mastermind behind the bombing, died in 2013 during a manhunt for the brothers in Watertown, Massachusetts.