The defendant, identified as 25-year-old Siale Angilau, died at a hospital hours later.
Cardwell and Jacobson witnessed the violent attack unfold. After emerging from the courthouse several hours after the shooting, they told reporters that Angilau jumped up from the defense table and lunged toward the witness stand, where it appeared he tried to punch the witness.
Authorities said the defendant charged the witness stand while holding a pen or pencil. At that point, the defendant was shot by a marshal several times in the chest.
"Everything was so fast," Cardwell said, adding that he thought he heard eight shots fired.
Angilau then fell to the floor, and Cardwell said the marshal kept firing.
"I thought, when is he going to stop shooting?" Cardwell recalled.
Cardwell said courtroom spectators were ordered to get down, and everyone crawled beneath the benches.
Angilau's trial was being heard in U.S. District Judge Tena Campbell's courtroom before a jury. 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 operations in the Salt Lake Valley over two decades. Court documents allege Angilau was involved in an incident where two deputy U.S. marshals were shot at, but not injured, in August 2007. The racketeering case also linked Angilau to several violent convenience store robberies between 2002 and 2007.
Angilau's trial was the first in the new courthouse at 400 South and West Temple, which opened for business April 14, and the last of a slew of TCG trials stemming from the 2010 indictment, said Melodie Rydalch, with the U.S. attorney's office.
Cardwell and Johnson said the witness, who appeared to be a jail or prison inmate, was testifying about the inner workings of the gang such as how it operated, how members were inducted and other specific details before Angilau, who was not restrained or in handcuffs, lunged toward him.
When Cardwell was asked about how he felt after the shooting, he said he had mixed emotions.
"Half of me is sad," he said. "You know, [Angilau's] mom had to see that. [But I wonder] what could he do to other people? Obviously, he has no heart."
Angilau was reportedly breathing when he was carried out of the courthouse on a stretcher, FBI assistant special agent in charge Mark Dressen said, but he died at about 2 p.m.
The witness, who was identified by defense attorney Steven Killpack as 31-year-old Vaiola Mataele Tenifa, was not injured.
Tenifa is currently serving up to 30 years at the Utah State Prison on 2001 convictions for robbery and aggravated assault. He has been paroled four times through the years, most recently in May 2012, according to parole authorities.
He faces a new charge of object rape, filed in September 2013 in Cache County's 1st District Court, and was charged last year in federal court with being a felon in possession of ammunition.
Because Tenifa was a cooperating witness, his identity was kept under wraps until about two weeks ago. Tenifa was not charged as part of the TCG indictments.
Angilau's attorney filed a motion last week objecting to the inclusion of Tenifa's testimony on the basis that it was too short of notice and Tenifa hadn't been properly vetted.
According to the motion, Tenifa was pulled into the case to implicate Angilau as an active member of the TCG. But defense attorney Michael Langford questioned Tenifa's "credibility, associations, crimes, possible conflicts of interests and purpose at trial."
Langford argued that "to properly defend himself against a potentially devastating witness with highly suspect integrity, credibility and firsthand knowledge," Angilau and his defense team needed time they were not given to prepare.
Langford declined to comment Monday on what had happened inside the courtroom as he left the federal courthouse Monday just after noon.
Cardwell's mother, Sandra Keyser, said she was the next witness expected to take the stand in the trial when the attack occurred. The woman, who now lives in Florida, said Angilau was 14 years old when he allegedly robbed her in December 2002, while she was working at a 7-Eleven near Liberty Park in Salt Lake City.
She said Angilau and some others entered the store after 10 p.m.
The defendant hopped over the counter, punched her in the face, then ran out of the store with cigarettes and beer.
"He didn't have to hit me, but he did that," Keyser said, adding that her interaction with Angilau was the beginning of his criminal "career."
Another woman, who asked not to be identified, told reporters gathered outside the building that she was also a clerk at a 7-Eleven store that was robbed in 2007. She had been subpoenaed to testify later that morning.
"I'm scared," she said, clutching her subpoena. "I'm just a little nervous right now."
Recalling the convenience store holdup, the woman said Angilau did not act alone.
"They were very, very violent," the woman said. "Very scary guys."
Angilau was an outstanding prep football player at East High School, says former coach Aaron Whitehead now at Olympus. Whitehead says Angilau was not only a dominating nose guard, but "as a person, as a kid, he was great," he said. "He was very likable. 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, because he's got a great family," he said.
Angilau was indicted on robbery charges connected to that 2007 robbery, to which he eventually pleaded guilty. In exchange, federal prosecutors dropped additional firearm and assault charges.
Angilau has been serving time at the Utah State Prison for 2008 convictions for obstructing justice and failure to stop at the command of an officer, according to the Corrections Department.
Before the news that Angilau had died, Judge Campbell declared a mistrial.
The judge noted in an order that the jurors, who witnessed Monday's shooting from just feet away, were "visibly shaken and upset," and would be prejudiced by the incident and unable to objectively rule in Angilau's trial.
"Defendant Siale Angilau apparently rushed and attacked a cooperating witness and was shot several times by law enforcement in front of the court and the jury," the order states. "After the shooting, a group of marshals continued to hold Mr. Angilau at gunpoint near the jury box while the jurors were still present in the courtroom."
Defendants are usually not restrained during jury trials, on the presumption that seeing a defendant in shackles would prejudice the jury.
After the shooting, the courthouse was locked down until about 12:30 p.m. All criminal cases were canceled, but security officers said that five civil cases that were on the Monday docket would resume.
Prison officials said Monday afternoon that the facilities in Draper and Gunnison will be on lockdown for the rest of the day as a security precaution, and no visitation will be allowed.
Tribune reporter Matt Piper contributed to this story.
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