The second week of Jabrai Jordan Copney’s murder trial opened yesterday with a full day of testimony that focused heavily on forensic evidence.

As prosecutors continued to present their case—aiming to prove that Copney shot Cambridge resident Justin Cosby in the Kirkland House annex—yesterday’s testimony centered on bullet casings, bloodstains, and fingerprints.

A string of police officers and forensic experts took to the witness stand to discuss DNA swabbing techniques, tests for the presence of human blood, and chemical checks for gunshot residue. The jury viewed some graphic evidence, including the blood-soaked T-shirt that Cosby was wearing when he died and up-close photographs of dried blood streaking the stairwell of Kirkland’s J entryway.

Yesterday also saw the end of the testimony of Jules E. Bolton, the 2009 Yale graduate who said in his initial appearance on Friday that he was robbed of three pounds of marijuana at gunpoint by Copney in 2008.

During his two days on the stand, Bolton said that he earned about $40,000 by selling marijuana at Yale and did not report that income on his tax returns.

Defense attorney John A. Amabile indicated on Friday in a dialogue before the jury entered the courtroom that he planned to cast Bolton’s failure to pay taxes on his drug profits as a sign that he is liable to lie on the witness stand.

Bolton recounted his extensive experiences buying, selling, and using marijuana. At one point, Amabile asked Bolton to identify the contents of a package.

“It looks like marijuana, but I’d need a closer inspection to be sure,” Bolton said. He then asked permission to remove the layers of plastic surrounding the package in order to get a clearer glimpse of the substance.

As the attorneys began to convene with the judge about whether Bolton could legally remove the wrapping, Bolton called out a suggestion.

“Maybe a sampling,” he offered. “I’d be absolutely certain.”

A police officer was called to open the package.

Katherine A. Carroll ’09 also took the stand yesterday to identify photographs of the Lowell House room in which she lived during her senior year at Harvard. The gun that prosecutors allege was used to kill Cosby was found by police under Carroll’s bed—allegedly stowed there, without Carroll’s knowledge, by former Harvard student Brittany J. Smith, one of Carroll’s blockmates.

Smith, who is dating Copney, has been indicted herself on charges that she hid the murder weapon and helped Copney and his accomplices flee to New York City after the crime. She is tentatively scheduled to be tried after Copney’s trial concludes.

After questioning Carroll about the photographs of her room and the police’s procedure in searching it, Assistant District Attorney Daniel J. Bennett ’85 asked, “Now, had you ever put a gun under your bed in a trash bag?” Carroll said no, leaving Bennett with no further questions for her.

—Xi Yu contributed reporting to this story.

—Staff writer Julie M. Zauzmer can be reached at jzauzmer@college.harvard.edu.