Italian prosecutors were investigating whether negligence played a part in Connor's death, focusing on four paratroopers who were around him at the time.
The US Army, however, was able to gain jurisdiction in the case, effectively halting the Italians' investigation.
The Italian authorities' autopsy was called off on October 3, just a day before it was scheduled to take place after the US asserted jurisdiction.
Connor is believed to have died from alcohol poisoning or asphyxia. Under Italian law, people must notify authorities if they see a person who is incapacitated, Stars & Stripes notes.
Without an autopsy, however, there is no evidence for Italian prosecutors to move forward with in the case, the lawyer for the four paratroopers that were under investigation, Stefano Grolla, told the outlet.
The definitive cause of Connor's death remains unknown, however.
According to reports from medical staff sent to Italian prosecutors and cited by Grolla, Connor and the four other soldiers were drinking when he became incapacitated. The other four laid him on his side in the bathroom, stepped away for a few minutes and found him unresponsive upon returning.
Connor was declared dead at a local hospital after repeated attempts to revive him.
Once Grolla was contracted to represent the soldiers, he said the US Army was relentless in its bid to take control of the situation, telling him, "Don't touch the body. Block everything."
"I can't. I'm only a lawyer," he reportedly told them.
Connor's death came just three days before his 25th birthday. His father, also named Kevin Connor, served 26 years in the Army. He told Stars & Stripes that authorities told him his son died of asphyxia or that he "choked to death."
"I understand how these things happen," he told the outlet, adding that he did not want to see the other paratroopers punished.