He stared at the backs of the heads of five men in white robes, seated with their lawyers at five long tables, one behind the other.
He wanted them to look at him; he tried to silently will them to look at him.
Turn around, turn around, turn around.
A defendant, his long beard dyed red, signifying his status as a leader, swung in his chair to talk to someone behind him. If he noticed Jenca standing behind the glass, he didn't let on.
"It was as if we weren't there," Jenca said. "As if I didn't matter."
Raging, he took his seat.
Darkness, then quiet
Jenca wasn't supposed to be at the World Trade Center on Sept. 11, 2001. His office as a security manager for Credit Suisse First Boston was 30 blocks away.
But after an airliner slammed into the North Tower, he was dispatched to lower Manhattan to check on the firm's employees at 5 World Trade Center.
On the way there, his wife, Lisa, a nurse, called him from the hospital. "What," Jenca snapped. "I'm very, very busy now."
"Don't go down there," Lisa implored, sputtering about a second plane.
"Listen," Jenca said impatiently, "you're probably just watching a replay. Calm down."
"No! Another plane just hit the second tower!" Lisa shouted.
Both towers were ablaze by the time Jenca arrived. Trained in emergency procedures as the firm's security expert, he looked for a mobile command center.
Over his shoulder, Jenca saw the South Tower start to collapse. He sprinted down Fulton Street, terrified that the building would land on him like a falling tree. As he turned onto Broadway, he tripped and quickly became engulfed by a gust of debris.
He couldn't breathe.
He remembers darkness, then quiet.
'I live it every day...'
Never returning to his job, Jenca now receives disability pay. His body still bears scars from being kicked and trampled. He has had two surgeries on his knee. He suffers back and neck pain, lost lung capacity, and trouble sleeping. He also suffers post-traumatic stress that can be triggered by something as innocent as a posting on Facebook.
For many survivors, Sept. 11 was not just a day; it has become a state of mind.
"I live it every day like it was yesterday," he said.
Jenca regularly trolls the Internet for news on the "9/11 Five," the defendants charged with mass murder and conspiring to commit the Sept. 11 attacks.
The Obama administration tried to move the trial to a civilian court in New York, but faced so much backlash that the matter returned last year to a military tribunal at Guantanamo.
Every few weeks, lawyers in the case take a charter flight to Guantanamo for pretrial hearings.
Each time, the Pentagon holds a lottery to select a group of survivors and victim relatives - five, plus a traveling companion for each - to go along. By law, "they have the right to attend proceedings," said Karen Loftus, director of the Victim and Witness Assistance Program at the Department of Defense.
Jenca was eager to go. He knew another Bucks County couple, Judi and Gary Reiss of Lower Makefield, were among the first survivors to make the trip, in July 2009. Judi, a mother of five who lost her bond-trader son Joshua, had told Jenca it was important to bear witness. "It made me feel that there will be justice," she recently recalled.
Jenca put his name in the lottery with 300 others.
In early October, he got the call.
A 'sensitive' letter
Soon after the flight touched down in Cuba on Oct. 21, the families were given a letter from lawyers for the 9/11 Five.
"While it is our duty to give the best representation possible to our clients, it is our intention to be sensitive to you and the many families deeply affected by the September 11th attacks," the lawyers wrote.
"They wanted to humanize their clients for us," Jenca said.
It would take some doing.
The Jencas were joined by six other people whose lives were ripped apart by 9/11.
There was a widow from Staten Island, whose police detective husband had been dispatched to work at the World Trade Center site and died in 2009 from lung cancer.
And the sister of a New York firefighter killed in the collapse of the North Tower.
And the Massachusetts sister and mother of a Navy commander, who was inside the Pentagon on the morning of the 11th.
And twin brothers whose older sister was on the plane that crashed into the Pentagon. One of them, Richard Costanzo, 48, of Hatfield, Montgomery County, said he felt the same sense of duty as Jenca.
"If people like me and Jim and others forget, how can we complain if the nation forgets," Costanzo said last week.
In the courtroom, Jenca estimates he was sitting 50 feet from the accused mastermind, Khalid Sheikh Mohammed, known at Guantanamo by the shorthand KSM. "His name is embedded in my mind," Jenca said. "Finally, I was that close to him."
KSM was a top al-Qaeda operative and planner, who called the 9/11 attacks, according to the Pentagon, his "life work." In a CIA prison, he was subjected to waterboarding, reportedly 183 times in one month.
Each defendant has a government-appointed lawyer for the tribunal before Army Col. James Pohl.
Jenca was shocked to see the attorney for Walid bin Attash, Cheryl Bormann, dressed in traditional Islamic garb, a black hijab covering her head.
One evening, the relatives took up the defense team's offer to meet them outside the courtroom. Jenca recalls a military attorney telling them that if an American soldier was taken prisoner and mistreated, wouldn't they want someone arguing in his or her defense?
Jenca shot out of his seat. "Do you think for one second our military men and women are treated with the same respect as we're treating these war criminals?"
"I believe in due process," he went on, "but don't expect for one second that your client would treat our soldiers in the same manner."
A flag for each family
The days inside the tribunal moved slowly.
Most of the court time was taken up by attorneys' motions. One involved forcing the prosecution to turn over classified information on torture at CIA "black sites" from 2003 to 2006.
Before heading home, each family was given an American flag that had flown at the base on the last 9/11 anniversary.
Today, Jenca's hangs in his family room, next to a framed portrait of him as a young Marine.
While the trial of the 9/11 Five may not begin for years, the Pentagon plans to keep bringing down families until everyone on the lottery list gets a chance. Officials will then start over again with anyone who wants to return.
Jenca is glad he went to Guantanamo. "It was gratifying for me to see justice is carried on," he said.
Would he go again?
"In a heartbeat."