Two things happened as the third week of testimony in the Boston Marathon bombing trial drew to a close Thursday..

The simple but deadly bomb-making prowess of the Tsarnaev brothers was firmly established.

And the grizzly life-destroying impact of their bombs was demonstrated as jurors were shown graphic autopsy photos of one of just one of  the three people killed in the attacks.

A medical examiner described the wounds of 29-year-old Krystle Campbell after the first bomb exploded near the marathon finish line April 15, 2013.

According to the Medical Examiner, there were wounds all over Campbell's body, including gaping wounds to her legs, third-degree burns to her back and numerous wounds from BBs and pieces of metal. She estimated that Campbell lived for up to a minute after the bombing.

One juror cried and wiped her face with a tissue as she looked at the photos.

Tsarnaev's lawyers have admitted that he and his late brother, Tamerlan, detonated the bombs, but they say Tamerlan was the mastermind.

Below is an account of the 14th day of testimony -- in reverse chronological order -- from WGBH News reporters, Emily Rooney, Phillip Martin, and Adam Reilly. 

UPDATED, 9:46 p.m.

While the big news in the trial of admitted Boston Marathon bomber Dzhokhar Tsarnaev Thursday was the gut-wrenching testimony about Krystle Campbell's death--the defense quietly continued its strategy of attempting to undermine the prosecution's credibility.

The strategy of Tsarnaev's defense team can be summed up in four words. Whenever possible--create doubt. On Thursday, that meant challenging the highly technical testimony of two FBI agents -- one specializing in the chemistry of explosives, the other in the mechanics of bomb making. Cross examining the first agent, the defense stressed that no explosive residue was found in Tsarnaev's dorm room at UMass Dartmouth.

Cross examining Agent Number Two, the defense asked several times whether the bomb parts recovered by the government had been tested for fingerprints. Repeated government objections kept the witness from answering--but the implication was clear: Dzhokhar's deceased brother Tamerlan was the bomb maker in chief.

Expect to hear more about fingerprint testing when the defense begins presenting its case next week.

5:04 p.m.

A medical examiner Thursday described the injuries sustained by Krystal Cambell, one of three victims of the Marathon bombing.  The testimony appeared to have had a major impact on jury members.
Krystle Campbell may have lived for up to a minute after sustaining horrific injuries during the attack of April 15, 2013.

That according to Dr. Jennifer Hammers, a medical examiner, who performed the autopsy. 

Hammers was the last witness of the day and she described in graphic detail the physical damage wreaked on 29-year-old Campbell’s  body by the explosion set off near the Boston marathon finish line.

Campbell died from blast injuries to her torso and to both the arteries and veins in her lower extremities.  Pieces of metal & pellets were taken from her body. 

The photos of her autopsy were shown jury members.  One of them —a blond woman in a striped blouse pressed a napkin to her face and her eyes glistened with tears.

Other jurors were also visibly shaken by the photos and testimony.  Jury members are bracing for more on Monday when the autopsy reports of 8 year old Martin Richard and 23 year old Lingzi Lu will be detailed.     

3:24 p.m.

The government had expected to call its last witness in the case against Dzhokhar Tsarnaev Wednesday afternoon, but now it seems that may not happen after all. .

The Tsarnaev jury is still hearing testimony from FBI agent Edward Knapp--who's been describing the inner functioning of the homemade bombs used by the Tsarnaevs in exquisite detail.

A few minutes ago, Knapp handed mock-ups of these devices to jurors--who passed them around and inspected them with varying degrees of interest.

While the government had expected to introduce evidence involving the three fatalities at the Marathon finish line today--it now looks as if Knapp might still be on the stand when the trial adjourns for the day.

2:02 p.m.

Testifying for the government, an FBI agent Thursday afternoon detailed how instructions from al Queda’s Inspire magazine, mirrored step by step construction of pressure cooker bombs set off by Dzhokhar and Tamerlan Tsarnaev at two sites on Boylston Street.   

FBI agent Edward Knapp says the similarity of the Boston bombs and the al Queda instructions -- "How To Build A Bomb In The Kitchen Of Your Mom" - - included suggestions for the best shrapnel that should be enclosed to cause maximum harm: bb’s and nails.

Agent Knapp said that his department had recovered thousands of pieces of bomb fragments and re-constructed the Marathon day explosives in order to understand how they were made. 

The FBI also recovered two unexploded pipe bombs from Laurel Street in Watertown.

These types of explosions are not difficult to make, according to testimony.

Knapp testified that the explosives used on Boylston Street in front of the Forum Restaurant and Marathon Sports required massive amounts of powder extracted from fireworks. They also relied on hobby fuses, and transmitters, and receivers that were purchased on-line and at a model car store in Malden. 

As far as making the bombs, Knapp told the court  “it's not that sophisticated, not that difficult” and he said that bomb making instructions are commonly available on the Internet.

12:00 p.m.

The prosecution is poised to rest its case against admitted Boston Marathon Bomber Dzhokhar Tsarnaev on a dramatic note--but so far, today's testimony has been uneventful.

The government plans to focus on the deaths of marathon bombing victims Lu Lingzi, Crystal Campbell, and Martin Richard -- and the testimony and evidence will likely be gut wrenching.

But so far, Thursday's proceedings have been highly technical -- with two FBI agents discussing the chemical and mechanical composition of explosives in great detail.

In a brief cross examination, the defense seemed to suggest that Dzokhar's deceased brother Tamerlan was the bomb maker--though its line of questioning was occasionally hard to follow.

This afternoon three medical examiners will each talk about one of the three fatalities at the finish line - starting with 8-year-old Martin Richard. Only his clothing will be entered into evidence.

Martin's mother Denise Richard is in court today.

9:00 a.m.

As the 14th Day of the Boston Marathon bomb trial opens, the government case in the U.S. vs Tsarnaev is winding down. Wednesday, FBI agents detailed  to the jury how materials for the explosive devices were obtained. 
The FBI used data from a GPS device owned by the Tsarnaev brothers to trace purchases of materials used to build the explosives that took three lives. 

By examining receipts left by Tamerlan Tsarnaev in his wallet, as well as store surveillance videos from a Target store in Watertown, FBI agents pieced together the chronology leading up to Marathon Day 2013. 

Tamerlan Tsarnaev, according to court testimony, spent close to 100 dollars for two backpacks on April, Sunday the 14th — one day before the big race. He can be seen in a video exiting from the Target store.  The timestamp read 4:07 pm. 

The defense has argued that Tamerlan was the Marathon bombing ringleader. And FBI Agent Christopher Derks seemed to buttress this argument in his testimony that it was Tamerlan who bought remote-controlled cars and a transmitter/receiver from a model car store in Malden used as bomb components. 

Befroe purchasing the knapsacks at Target, Tamerlan had raided Walmart store shelves in New Hampshire for bb’s and pressure cookers.  And the FBI says he constructed the devices in his apartment on Norfolk Street in Cambridge—that he shared with his wife and child.

Today a bomb expert will be in court to explain --step by step-- how the explosives were made.