A Suffolk County homicide prosecutor today told jurors that a friend of 64-year-old Richard Stroman brutally stabbed him almost two dozen times and left him to die in a pool of his own blood.

LARRY NELSON (D.O.B. 1/5/58) is charged with first-degree murder for Stroman’s homicide at the victim’s Elm Hill Avenue apartment on the afternoon of Oct. 7, 2007. His trial began in Suffolk Superior Court this morning.

In her opening statement, Assistant District Attorney Gretchen Lundgren told jurors that Nelson went to Stroman’s apartment on the day of the stabbing.

While at the victim’s home, Nelson – “who was 15 years younger than the victim, inches taller, and 75 pounds heavier,” the prosecutor said – allegedly began stabbing and slicing the victim in the head, neck, chest, back, arms and hands.

Some wounds measured five to six inches deep, Lundgren said, “striking major organs and an artery.”

“No matter what happened in that front hallway, the defendant’s reaction was completely out of proportion,” Lundgren said.

During the course of the stabbing, Lundgren told the court, Nelson seriously injured his right hand and began bleeding such that he left a trail of blood from the front of the apartment to the victim’s bedroom, the bathroom, and a set of stairs out the building’s back door.

Nelson later sought medical attention for his wounds at a hospital in Cambridge, Lundgren said, and told police that he had been the victim of a robbery by a man with a knife in either Cambridge or Somerville. She told jurors that Nelson’s story to Cambridge and Somerville police officers “kept changing, evolving” and that “they knew he was covering something up, but didn’t know what.”

On Oct. 12, 2007, one of Stroman’s neighbors contacted authorities after detecting a strong odor coming from his apartment. When Boston Police gained entry to the residence, they found the victim lying dead in his hallway in a pool of blood. An autopsy later revealed that he had been stabbed 20 times.

Boston Police criminalists, who collected and analyzed blood leading away from the victim’s body, determined that there was blood on the scene that belonged to someone other than Stroman.

After a far-reaching investigation by Boston Police homicide detectives led to Nelson as a suspect, detectives interviewed Nelson about his role in the stabbing.

“The defendant trotted out the robbery story,” Lundgren said. During the interview, “he remained calm, cool and collected under pressure,” and denied killing Stroman, she said. Nelson was asked to voluntarily provide detectives with a DNA sample, Lundgren said. Within weeks, she said, investigators were able to match Nelson’s DNA to the blood trail that was found in Stroman’s apartment. Nelson was arrested on April 4, 2008, and subsequently charged with Stroman’s murder.

“The defendant murdered Richard Stroman, and has done nothing since then except to lie,” Lundgren said.

Nelson is represented by attorney John Palmer. Testimony is ongoing before Judge Judith Fabricant in courtroom 817 of Suffolk Superior Court.