"We expect he will make a full recovery," Lanier said.
Earlier, CNN's Chris Lawrence reported that physicians were expected to begin determining Tuesday whether the officer would be able to keep the limbs.
Also, Lanier said at the news conference that there's "no doubt in my mind" that the officers responding to the shooting "saved numerous lives."
2:11 p.m. ET -- More from the news conference: Alexis arrived in the Washington area on or about August 25, staying in hotels, said Valerie Parlave, assistant director in charge of the Washington FBI field office.
He most recently stayed at a Residence Inn in southwestern Washington, D.C., beginning around September 7, she said. Anyone who contacted him during that time should contact the FBI, she said.
2:08 p.m. ET -- FBI and other officials have begun a news conference in Washington, updating reporters on the investigation.
Alexis entered the yard's building 197 -- where the shooting took place -- with a shotgun, and investigators believe he obtained a handgun inside the building after he started shooting, Valerie Parlave, assistant director in charge of the Washington FBI field office, said moments ago at a news conference. This confirms what federal law enforcement sources said earlier.
2:01 p.m. ET -- U.S. Defense Secretary Chuck Hagel is ordering a worldwide review of physical security measures at all U.S. military installations in the wake of Monday's shooting, a senior Pentagon official said Tuesday, according to CNN's Barbara Starr.
Hagel will order the military to look at all existing security measures to see if they are sufficient and to determine what other measures may be needed, the official said.
At the same time, the Pentagon is still trying to determine what it needs to do to begin a parallel review of security clearances and access standards for contractors and other employees, according to a Defense Department official. Some elements of clearance procedures are handled by other parts of the government so coordination will be required, but the official said it's expected some review of that element will also take place.
This follow an earlier confirmation from the Navy that it was beginning a similar physical security review at all of its installations.
1:13 p.m. ET -- Alexis was "having problems sleeping" and was "hearing voices," a source with direct knowledge of the Navy Yard shooting investigation said, according to CNN's Deborah Feyerick. The source said Alexis exhibited signs of mental problems in recent months and tried to get help at a Veterans Affairs facility in Rhode Island. He worked as an information technology contractor in Newport, Rhode Island, in August.
The source also said that the 9/11 attacks caused Alexis to leave his home in New York City. He could not deal with the attack and essentially wandered from place to place: San Diego, Texas, and overseas, the source said.
His father told Seattle police in 2004, after Alexis was arrested there, that his son was suffering from post-traumatic stress disorder after taking part in 9/11 rescue efforts, according to police records.
Earlier Tuesday, law enforcement sources told CNN that Alexis recently made contact with two Veterans Administration hospitals for apparent psychological issues.
12:44 p.m. ET -- A gun store in northern Virginia, Sharpshooters Small Arms Range in Lorton, released a statement in response to inquiries about Alexis. An FBI source with firsthand knowledge of the Navy Yard shooting investigation told CNN that one of the weapons Alexis is accused of using was purchased recently at a northern Virginia store. The Sharpshooters statement, shown below, does not affirm that it sold Alexis the gun.
"Sharpshooters Small Arms Range has been and continues to fully cooperate with law enforcement authorities in their investigation of the events at the Washington Navy Yard," the store said. "In light of the many questions surrounding the event, it is not appropriate to provide any comment at this time, except to affirm that Sharpshooters fully complies with all requirements to conduct background checks on all potential purchasers as required by law, and to further affirm that all purchasers are required to comply with all laws concerning allowed purchases."
12:06 p.m. ET -- The Navy began proceedings in 2010 to give Alexis a general discharge from the Navy Reserve because of military and civilian disciplinary issues, but eventually gave him an honorable discharge in January 2011 because of a lack of evidence supporting the sterner measure, a U.S. defense official told CNN's Barbara Starr.
The disciplinary issues include at least eight instances of misconduct while on duty, the official said.
The attempt to give him a general discharge began after the Navy learned of his 2008 arrest in Georgia (on suspicion of disorderly conduct) and his 2010 arrest in Texas (on an allegation that he fired a gun through the ceiling of his apartment), the official said.
Alexis was a full-time Navy reservist from mid-2007 to January 2011.
11:53 a.m. ET -- We now have all the slain victims' names. The latest five to be released by Washington police are:
• Arthur Daniels, 51
• Mary Francis Knight, 51
• Gerald L. Read, 58
• Martin Bodrog, 54
• Richard Michael Ridgell, 52.
On Monday night, Washington police released the first seven names:
• Michael Arnold, 59
• Sylvia Frasier, 53
• Kathy Gaarde, 62
• John Roger Johnson, 73
• Frank Kohler, 50
• Kenneth Bernard Proctor, 46
• Vishnu Pandit, 61.
11:46 a.m. ET -- It's back to baseball Tuesday for the Washington Nationals, who postponed a Monday game as the organization allowed the Navy to use one of its parking lots as a site where Navy Yard evacuees could reunite with their loved ones.
The Nationals will wear their "Patriotic Blue" jerseys in the first game of a double-header with the visiting Atlanta Braves, the team said. The first game, to start at 1:05 p.m., is the makeup for Monday's postponement.
The Navy Yard is just blocks from Nationals Park.
11:30 a.m. ET -- Navy Secretary Ray Mabus on Tuesday will "order reviews of all physical security at all Navy and Marine Corps installations," a U.S. Navy official told CNN's Barbara Starr.
"The first will be a quick look to ensure all physical security requirements are being met. The second will be a deeper review to ensure the right physical and personal security requirements are in place," the official said.