Angilau died at a hospital from multiple gunshot wounds to the chest at about 2 p.m. Monday.
Court documents allege Angilau and fellow gang members took part in a number of armed robberies and assaults over a five-year period.
But years before he was charged with racketeering or had spent time in prison, Angilau was an outstanding prep football player at East High School, said former coach Aaron Whitehead now at Olympus. Whitehead said Angilau was not only a dominating nose guard, but also "as a person, as a kid, he was great."
"He was very likable," Whitehead added. "He was very coachable."
Whitehead said he lost touch with Angilau, although he was aware of his troubles with the law.
"I am heartbroken for his family," Whitehead said, "because he's got a great family."
Angilau's attorney, Michael Langford, said Tuesday that he spent a lot of time with his client as he defended him over four years during the racketeering case.
Monday marked the first day of testimony in what was scheduled to be a two-week trial.
"[Angilau] always treated my defense team and me with the utmost respect," Langford told The Salt Lake Tribune. "It was a tragic event for everyone involved. My thoughts right now are with Siale's loved ones and everyone else affected by this."
There was an outpouring of support for Angilau from the Pacific Islander community across social media. Hashtags like #RIPSialeAngilau circulated on Twitter.
"Heart is aching and heavy ... in disbelief that I've lost my nephew so tragically in so little time," Koli Pilivi posted.
Another Angilau is currently facing serious criminal charges in state court. Siale Angilau's younger brother, 21-year-old Vilisoni Tuino Angilua, was charged last year in 3rd District Court with first-degree felony murder for the alleged gang-related shooting of 19-year-old Sione Fakatoufifita outside a Salt Lake City Maverik store.
On April 13, 2013, Vilisoni Angilua and other gang members allegedly pursued Fakatoufifita through the Glendale area, until they arrived at the store at 1680 S. Redwood Road, where police allege that Vilisoni Angilua found Fakatoufifita and shot him.
No trial dates have been set in that case.
Despite Monday's violent episode at Salt Lake City's new federal court building which opened for business at 400 South and West Temple on April 14 it appeared to be business as usual there Tuesday. The judge who presided over Angilau's trial was back to work and no extra security officers were visibly present.
The U.S. marshal who shot Angilau was on paid administrative leave.
Siale Angilau's trial was being heard in U.S. District Judge Tena Campbell's courtroom before a jury of 12, plus two alternates the first trial held in the new facility.
Siale Angilau was among 17 TCG members and associates indicted on racketeering charges in May 2010.
Federal prosecutors allege the gang committed murders, robberies and assaults to expand its operation in the Salt Lake Valley over two decades.
Court documents allege Siale Angilau was involved in an incident where bullets were fired at two U.S. marshals in August 2007, for which he had been serving time at the Utah State Prison. The racketeering case also linked Angilau to several violent convenience store robberies between 2002 and 2007.
Of the 16 other TCG members indicted in the racketeering case, six defendants took plea deals, six were convicted in September 2011 after a five-week trial, two were acquitted and charges were dismissed against two defendants in 2012.
Defense attorney Steven Killpack said it was his client, 31-year-old Vaiola Mataele Tenifa, who was on the witness stand when the attack occurred. But Killpack said Tuesday he did not witness the shooting because he had briefly left the courtroom to retrieve a file from his car.
Tenifa, who is serving up to 30 years at the Utah State Prison on 2001 convictions for robbery and aggravated assault, was not injured in the attack. Through his attorney, Tenifa on Tuesday declined a request for an interview.
Tenifa, according to court documents, is "a former, and recent, member of TCG" who agreed to cooperate with federal prosecutors.
But Siale Angilau's attorney filed a motion last week objecting to the inclusion of Tenifa's testimony on the basis that, among other things, Tenifa had a "probable personal bias against Mr. Angilau."
According to the Langford's motion, Tenifa was pulled into the case just two weeks before the start of the trial to implicate Angilau as an active member of the TCG.
"The cooperating witness [Tenifa] has an extensive criminal history, a tenuous or third-party relationship to the defendant, a relationship with the Tongan Crip Gangs distinct from Mr. Angilau, and probable personal bias against Mr. Angilau," Langford added.
Langford argued the defense team needed time to prepare which they were not given "to properly defend himself against a potentially devastating witness with highly suspect integrity, credibility and firsthand knowledge."
Although the jurors hearing Siale Angilau's case were excused after the shooting, Judge Campbell signed an order Monday afternoon extending the term of service for the jury "until counseling is no longer needed."
In reaction to the courthouse shooting, the state prisons in Draper and Gunnison were put on lockdown Monday as a precaution.
By Tuesday afternoon, the lockdown had been lifted from some areas of the Draper prison, including the women's facility. Other inmates in Draper and Gunnison are being given time out of their cells and access to telephones, but visitations remained suspended, according to the Utah Department of Corrections.
Reporter Tom Harvey contributed to this story.
Twitter: @jm_miller, @mikeypanda