Using the legal theory that holds a...

Using the legal theory that holds a person accountable for the “natural and probable consequences” of his acts, a prosecutor told jurors Wednesday that gang member and private school student Ari Tomasian is responsible for the fatal stabbing of Abtin Tangestanifar at a “Sweet 16” birthday party because he started a street fight that ended with a killing.

“He probably was the stabber--at least, one of the stabbers,” Deputy Dist. Atty. Darrell Mavis said in opening statements. “He viciously beat Abtin, a natural result of which was that Abtin died.”

Defense lawyer Melvyn Douglas Sacks countered that Tangestanifar, 17, died in a street brawl among drunken teenagers. To this day, he said, nobody knows who stabbed the victim.

“We have a mystery as to who’s liable for the death of Abtin Tangestanifar,” Sacks said. “You’ll hear witness after witness create a doubt in your mind as to what transpired.”

Of the six defendants who were originally arrested in the case, two were exonerated during a preliminary hearing after witnesses changed or clarified their testimony. Prosecutors asked that the charges against them be dropped.

Another defendant was tried in Juvenile Court, where he was convicted of assault. Two others pleaded no contest to manslaughter charges.

Tomasian, the last defendant, is on trial in Van Nuys on a murder charge.

The strongest evidence against him is the recovery of the victim’s blood on the jacket he was seen wearing that night. Defense lawyers are trying to keep that evidence away from the jury.

Prosecutors said witnesses will testify that they saw Tomasian with a knife, heard him say before the fight that “men fight with weapons,” heard him yell his gang’s name during the fight and heard him say he wanted to stab the victim’s friend too. An enormous tattoo of his gang nickname, “Mr. Whiner,” and his gang’s name, Jef Rox, covers his back.

But the conflicting accounts of teenage witnesses continue to hamper the efforts of police and prosecutors trying to find out exactly what happened the night of May 30, 1998.

Authorities say that between 100 and 150 high school juniors and seniors, many of them from private schools, were celebrating a girl’s 16th birthday in a million-dollar Encino home.

According to court records and testimony, one of the guests was drunk and obnoxious. His friend, Tangestanifar, escorted him out.

Word of the disturbance spread and authorities allege that Tomasian told the hostess that he was going to start something with the troublemakers when they got outside.

“It was based on drunks, out of control, and a verbal altercation erupted into a fistfight,” defense attorney Sacks said. “My client, acting immaturely, in a bravado manner, was going to teach them a lesson.”

Tomasian and others are alleged to have confronted Tangestanifar and his friend and called out the common street challenge: “Where are you from?”

Mavis, the prosecutor, said Tangestanifar, a popular Taft High School student, tried to smooth things over by insulting the Bloods, a gang he mistakenly thought was an enemy of Tomasian’s gang.

Mavis said Tomasian and his friends responded by attacking Tangestanifar and his friend.

“They beat him, they punched him, they kicked him,” Mavis said.

When it was over, Tangestanifar had been stabbed 11 times. He was pronounced dead at Northridge Hospital Medical Center.

Sacks denied Tomasian stabbed Tangestanifar, intended to stab him or even knew anyone was armed. He said the fight was not gang-related.

He pointed out that a knife found in a car that Tomasian rode in, which authorities believed was the murder weapon, did not have Tomasian’s fingerprints.