Keith Brunjes and his best friend were hanging out watching the HBO prison series “Oz” one day in 2008 when they decided to get homemade tattoos, the kind depicted on the show. They bought ink at a Michaels arts and crafts store, and Mr. Brunjes studied up on the subject.

Mr. Brunjes, 18, said he first gave his friend a lightning-bolt tattoo in May 2008, and then a star, using ink, a needle and thread. About a month and a half later, he said, he gave him a third one on his right upper thigh: a swastika. The two friends did not discuss why.

“I didn’t ask about it,” Mr. Brunjes said. “He wanted it.”

Mr. Brunjes made his comments on Tuesday during his testimony in the hate-crime trial of the friend, Jeffrey Conroy, a Long Island teenager charged with fatally stabbing an Ecuadorean immigrant in Patchogue in November 2008. The authorities say Mr. Conroy and six other teenagers attacked the immigrant, Marcelo Lucero, in a wave of racially motivated assaults and attempted assaults on Latino men on eastern Long Island.

The case is being heard in State Supreme Court here in Suffolk County, before 12 jurors and 4 alternates. Eight are men, and eight are women. One is black, one is Hispanic and the rest are white.

Mr. Conroy’s feelings about white supremacy have become a crucial element of the case, the first trial for murder as a hate crime on Long Island since the state’s hate-crime law was enacted in 2000.

A Suffolk County prosecutor, Megan O’Donnell, told jurors last week that Mr. Conroy’s views on white supremacy were evident in the tattoos on his body and in the statements he made to others. Shortly after Mr. Lucero’s stabbing, Steve Levy, the county executive, called the seven defendants white supremacists.

Mr. Brunjes’s testimony on Tuesday appeared to raise more questions than answers about Mr. Conroy’s mind-set.

Mr. Brunjes, who has known Mr. Conroy since they were both about 8 years old, said he and Mr. Conroy did not have any conversations about why Mr. Conroy wanted a swastika, and he also testified that Mr. Conroy did not discuss the meaning of the lightning bolt. When Mr. Brunjes modified the lightning bolt tattoo, it resembled the logo of the Gatorade sports drink, Mr. Brunjes said in court.

But another young friend of Mr. Conroy’s testified on Tuesday that Mr. Conroy came to her house about a month before the stabbing and showed her the lightning bolt. The friend, Alyssa Sprague, 17, told him at the time that she thought it was the Gatorade logo. “He said, no, it was white power,” Ms. Sprague testified.

For the first time, the jury was shown photographs of the swastika tattoo and Mr. Conroy’s other tattoos, on a large screen that was visible to jurors and most of the courtroom gallery, where relatives and friends of Mr. Conroy and Mr. Lucero were seated.

After Mr. Brunjes gave Mr. Conroy the swastika tattoo, Mr. Brunjes testified, Mr. Conroy told him, “If I ever go to jail, I’m screwed.”

Mr. Conroy, now 19, has pleaded not guilty to second-degree murder as a hate crime as well as other charges. He was 17 when Mr. Brunjes gave him the swastika, which Mr. Brunjes described as being about one inch by one inch.

Mr. Conroy’s father, Robert Conroy, said in an interview last week that he did not know that his son had the swastika tattoo on his leg, and that if he had known, he would have taken his son somewhere to have it removed. He said his son did not believe in white supremacy and did not fully understand the symbol’s meaning and history when he got the tattoo.

“I was so mad when I found out that he had this,” Robert Conroy said. “He doesn’t wear it proudly. It was just kids being stupid.”

Mr. Conroy’s lawyer, William Keahon, has made it a point during the trial to have the young men and women who testify list, one by one, Mr. Conroy’s black and Hispanic friends. Asked outside the courtroom if his client had racist tendencies, Mr. Keahon responded, “Absolutely not.” He described the tattooing as “two young kids acting like jerks.”

Under cross-examination, Ms. Sprague told Mr. Keahon that she first spoke with a detective about the case in November 2008, shortly after the stabbing, but did not mention Mr. Conroy’s white-power statement at the time. She said she first told the prosecutor about it two weeks ago.

A Hispanic man who prosecutors say was chased by the seven teenagers earlier that evening in Patchogue also testified on Tuesday. The man, Hector Sierra, 57, who was born in Colombia, said he was walking home from his job as a waiter about 11:30 p.m. when he noticed a red or brown sport utility vehicle drive slowly past him. The vehicle stopped and four people stepped out and began running toward him, Mr. Sierra testified. “They caught me from behind and started punching me,” Mr. Sierra said. He escaped serious injuries.

Mr. Sierra said he did not get a clear look at the attackers’ faces, and he did not identify Mr. Conroy as one of them. Prosecutors have charged Mr. Conroy and the six other defendants with second-degree attempted assault as a hate crime against Mr. Sierra. They say that the seven teenagers that night were riding in a red S.U.V.