Ensign Aquino was a Starfleet engineering officer assigned to Deep Space 9 under the command of Commander Benjamin Sisko. He was barely knew by Chief Miles O'Brien who gave him, "Just the welcome aboard, if you need anything speech."
While Chief O'Brien and Neela investigated a tritanium source in a deactivated power conduit on level twelve, section eight, they found the tritanium remains of O'Brien's EJ7 interlock as well as organic remains. Doctor Bashir later confirmed that the organic remains were from Ensign Aquino. During the autopsy, after Bashir reconstructed the victim's DNA, he discovered plasma disruption in the cellular membrane which suggested he was exposed to a direct energy discharge before he was placed in the conduit. A probable source for the discharge was a phaser.
On the night of his death, Aquino took a turbolift to level three after finding that a sensor detects an anomaly in the security net near pad C. He interrupted Neela, who was attempting a bypass of the net with a security bypass module, who then murdered him with a phaser. She stole a EJ-7 interlock and placed it near Aquino in a conduit she deactivated. Clear of the conduit, she re-activated the conduit, destroying the evidence.
Covering her tracks, Neela crafted a story. She altered Aquino's logs, so that it seemeed that he had discovered a plasma flow irregularity in the conduit and went to fix the relay. While fixing the conduit, which he had de-activated, the computer would re-align the flow regulator, activing the conduit, and killing him instantly. Investigators would rule his death as an accident. However, there were flaws in the story, which ultimately led to its unraveling. One of these was that in Starfleet culture, it was unheard of for a subordinate to take an engineering tool without asking the department head. The other was the turbolift records, which showed he was heading to the runabout pads and not to the conduit.