Last Concert for a Grateful Dead Fan : Law Enforcement: The parents of a Fountain Valley teen-ager who died after being arrested have retained an attorney and a pathologist after a coroner’s report blamed neck injuries for his death.

As a sophomore at UC Santa Barbara, Patrick Shanahan loved to crank up his stereo system and blast records of Jimi Hendrix, Pink Floyd and his favorite group, the Grateful Dead. He often grumbled when the dormitory adviser asked him to turn the volume down, his friend Robert Jarrett recalled Friday.

“Music was really a big part of his life,” Jarrett said.

It was Shanahan’s loyalty to the Dead that drew him and Jarrett to the group’s concert Dec. 10 at the Forum in Inglewood. But there, after seeing the Dead perform for the 24th time, Shanahan died after being arrested by Inglewood police.

An autopsy report disclosed Thursday that the 19-year-old Fountain Valley youth died from neck injuries suffered when he was taken into custody by officers who suspected that he was high on drugs. Listed as contributing factors in his death were “multiple injuries and acute LSD intoxication.”

A police report of the incident also indicates that officers placed Shanahan in a chokehold--a method of restraint that some law enforcement agencies, including the Los Angeles Police Department, have outlawed unless an officer is confronted with the threat of death or serious injury.

The case is under investigation by the Los Angeles County district attorney.

Shanahan’s parents were en route Friday to Orange County from New Hampshire, where they buried their son last week. To conduct their own investigation, they have hired Lawrence Trygstad, a Los Angeles attorney, and Dr. Irving Root, the senior pathologist with the San Bernardino County coroner’s office.

Trygstad says he expects the family to file suit against the police once Root completes a follow-up autopsy.

“This sounds pretty severe,” Trygstad said. “The police were saying that this was a drug-related death. Based on what I know, they used excessive force.” The attorney said the autopsy revealed that Shanahan’s trachea was crushed.

Trygstad says he has spoken to about 20 witnesses, many of whom came forward after reading a flyer that was distributed at a series of Dead concerts in Oakland.

Inglewood police officers refused to comment Friday. But department officials have previously denied that officers used excessive force against the college student.

Jarrett described Shanahan as a youth disillusioned with the pollution and hubbub of Southern California. He had recently learned to surf, and had talked about changing his major from business to forestry so he could become a park ranger.

Shanahan had also experimented with marijuana and LSD, according to Jarrett.

“We took acid together a couple times at college,” Jarrett said. “He smoked pot, but he wasn’t heavily into it.”

Jarrett said Shanahan sometimes complained of being hassled by police. Records show that Shanahan’s driver’s license was suspended for three years last June after his arrest on a drunk-driving charge in Westminster.

But others who knew Shanahan described him as a good-hearted achiever.

“I watched him grow up, and he called me Uncle Joe,” said Joseph Panarese, a teacher at Goffstown High School in New Hampshire, which Shanahan attended before transferring to Fountain Valley High School. “He was the typical All-American teen-ager: He was very bright, he did well in school and he enjoyed life.”

Mike Kasler, principal of Fountain Valley High, recalled that Shanahan was a B-plus student who excelled in foreign languages and for two years was a member of the wrestling team. He graduated with honors in 1988.

“Even though he graduated a few years back, we still consider him one of our own,” Kasler said. “It is such a tragedy for someone so young and with so much potential to die like that. We feel for the family. It’s a shame. It’s a tragedy.”

The night before the Grateful Dead concert, Jarrett stayed over at the Shanahan home. He said he remembers staying up late talking with Shanahan and his parents about what the two youths were going to do with their lives.

The next evening, Jarrett said, he and Shanahan arrived at the Forum several hours before the concert and spent time shopping for Christmas presents at several T-shirt and novelty stands set up in a nearby parking lot.

After entering the arena together, the two friends sat together and listened to the show’s first hour. When Shanahan returned from intermission, Jarrett said, he appeared “worried, bugged out.” Jarrett said he did not suspect at the time that Shanahan--dressed in a tie-dyed shirt, jeans and white tennis shoes--might have taken drugs.

As they were dancing in an aisle during the second half of the concert, Shanahan suddenly walked away without explanation. Jarrett said he followed and watched Shanahan head toward the stage, then turn up the aisle toward an exit. When Jarrett ran up to him, Shanahan pushed him away.

“He was waving his hands,” Jarrett said. “He didn’t say anything. I thought he was mad at me and that he wanted to be on his own.”

Shanahan then walked away and Jarrett said he never saw him again.

Witnesses interviewed by The Times said Shanahan was subsequently beaten by police officers after he kicked over a plastic crowd barricade.

According to the police report, however, this is what happened after the concert ended:

An officer on patrol saw Shanahan standing with his body rigid and a blank stare on his face. The youth didn’t respond to questions, the report says, and he suddenly dropped to his knees and started yelling and laughing.

When he resisted the officer’s effort to handcuff him, two more officers were called to assist. Shanahan started kicking and “trying to bite any part of an officer that was near his mouth,” the report states.

After Shanahan was wrestled to the ground, he broke free from the officers and started to stand. Then one officer, according to the report, “placed him in a carotid control hold.”

The report says Shanahan continued to struggle as three officers got on top of him and others bound his legs with restraints. Eventually he stopped struggling but continued yelling, the report says. Officers put the youth in the back seat of a patrol car and headed for the Inglewood police station--until they noticed that Shanahan had stopped breathing.

They changed course and took him to nearby Daniel Freeman Memorial Hospital, where Shanahan was pronounced dead.