In his opening statement yesterday, prosecutor Rahsaan Hall said Rosa and the group of men, some of whom were underage, entered the Lansdowne Street club and gathered in an area reserved for people 21 and older.

"When they were asked to leave, a verbal altercation ensued," Hall told jurors. The argument continued until security escorted the group out of the club.

"As they were being escorted out of the nightclub, this defendant and some of his friends became physically combative," Hall continued. As Viera tried to calm the two groups outside the club, "this defendant walked behind a group of his friends, then stepped around his friend and lunged at Craig Viera, stabbing him in the upper-left abdomen."

Within minutes, Hall said, security staff and police officers working a detail in the area found Rosa and a knife he dropped. Viera spent three days in Beth Israel Deaconess Medical Center before returning to his home in Framingham, Hall said, unaware his stab wound was a ticking time bomb.

"That cut this defendant inflicted cut Mr. Viera's liver and his liver became distended and grew to three times the size of a normal liver," Hall said.

Viera's enlarged liver pressed against a major artery, causing blood clots in his legs, one of which moved through his bloodstream to his lungs.

"You'll hear the testimony of witnesses who will tell you that but for this stab wound this defendant inflicted, Mr. Viera would be alive today," Hall said.

Defense attorney John Hayes, however, argued the evidence shows his client could not possibly have stabbed Viera since the victim's blood wasn't found on the knife or Rosa's clothes.

"This case really starts with the fact that the blood on the knife and the defendant's clothing was not Craig Viera's blood, but was his own blood," Hayes said. "(It's) from that perspective, which is absolutely inconsistent with Oscar Rosa stabbing Craig Viera that night (I want you to consider the evidence.)"

The case was fatally flawed from almost the first moment, Hayes said, because after Rosa's quick arrest, police performed virtually no further investigation.

"It was so obvious to everybody he had to be the person, and it's that assumption that contaminates everything that happened after that," he said. "The police really didn't collect much evidence, and what they did collect was lost."

Several people took the stand yesterday, including Viera's mother, Sybil Viera, who described the day he died.

The day before he died, she said, her son tried to follow doctor's orders to try to keep active by walking, and even walked "with great difficulty" nearly two blocks to the bank. The next morning, "he was very slow.

"I put Craig's breakfast in front of him, and all of a sudden, his head dropped and it stayed like that for maybe a minute, like he was in a trance, and then he woke up and said, 'Mom, what happened?"' she said.

After refusing her offers to call 911 and his doctor, Viera tried to sit on the couch, but was clearly having difficulties, she said.

"His arm shook and his head dropped to one side. One eye stayed open and the other eye closed," she said. "I gave him mouth-to-mouth, and his body jumped twice. In my heart, I knew when his body jumped, no matter how much air I breathed it wouldn't help."

Also taking the stand yesterday were several Boston Police officers, who said they saw a fight in front of the nightclub, several men running from the area and Rosa drop an object just before his arrest.

Rosa's trial will resume today in Suffolk Superior Court.