Washington Navy Yard reopens 3 days after massacre

Updated at 8:44 a.m. ET

WASHINGTON The Washington Navy Yard began returning to nearly normal operations three days after it was the scene of a mass shooting in which a gunman killed 12 people.

The Navy installation re-opened at 6 a.m. Thursday. Traffic was blocked from reaching the main gate for a time because a tractor-trailer tried to make a U-turn, and its load shifted.

Navy spokeswoman Lt. Cmdr. Sarah Flaherty said Thursday will be a regular work day, except for Building 197, where the shootings occurred, and the base gym. She says the gym is being used as a staging area for the FBI to investigate Monday's rampage in which former Navy reservist Aaron Alexis gunned down 12 people before being killed by police.

Employees retuning to work Thursday said they still felt unsettled about what happened.

"It's a little surreal I guess," said Brooke Roberts, an engineer who works across the street from the building where the shooting happened.

"You don't think this sort of thing can happen to you at your workplace, so you're just not prepared for it, regardless," he said as he walked by a blocked off gate he is accustomed to using to enter the Navy Yard. He described himself as feeling "still unsettled," noting the blocked off entrance.

"It's still not quite normal, and it probably won't be for some time," Roberts said.

Barbara Smith said she was feeling apprehensive, walking toward the Navy Yard entrance.

"But, you know, I have to work, and I'm trusting that they're taking care of what needs to be taken care of," she said.

Law enforcement officials are still trying to determine a motive for the shooting. Officials have said the 34-year-old gunman was grappling with paranoia, hearing voices and convinced he was being followed.

Sources told CBS News that Alexis left behind two short phrases on the side of the shotgun used in the massacre.

One of the messages scratched into the gun's metal reads, "Better off this way." The other is more cryptic: "My ELF weapon."

Investigators don't know what the etchings mean. "ELF" might be a reference to "extremely low frequency" radio waves used by the Navy to communicate with submarines.

It also may relate to a strange incident which happened six weeks ago in Newport, R.I.

A month before the shootings, he complained to police in Rhode Island that people were talking to him through the walls and ceilings of his hotel room and sending microwave vibrations into his body to deprive him of sleep.

On Wednesday, the Department of Veterans Affairs told lawmakers in Congress that Alexis visited two VA hospitals in late August complaining of insomnia, but that he denied struggling with anxiety or depression or had thoughts of harming himself or others.

On Aug. 23 he visited an emergency room at the VA Medical Center in Providence, R.I. He made a similar visit five days later to the VA hospital in Washington.

Also on Wednesday, families began claiming the bodies of their loved ones from the medical examiner's office in Washington.