A former US naval reservist killed 12 people in a shooting rampage at a military base in the heart of Washington on Monday, before himself being killed in a shootout with police.

A former US naval reservist killed 12 people in a shooting rampage at a military base in the heart of Washington on Monday, before himself being killed in a shootout with police.
  
Police identified the alleged gunman as Aaron Alexis of Fort Worth, Texas, who served in the Navy from 2007 to 2011 before becoming a defense subcontractor for computer giant Hewlett-Packard.
  
US authorities probing the shooting spree at Washington's Navy Yard, which also injured eight, said that the gunman appeared to have acted alone. "We do now feel comfortable that we have the single and sole person responsible for the loss of life inside of the base today," police chief Cathy Lanier said late Monday.
  
The Federal Bureau of Investigation appealed to the public for information on the 34-year-old, whose military service was marked by disciplinary problems and who reportedly had once been arrested but not charged in Texas for shooting a bullet through his apartment ceiling.
  
"No piece of information is too small. We are looking to learn everything we can about his recent movements, his contacts and his associates," said Valerie Parlave, assistant director of the FBI's Washington field office.
  
The FBI released a photo of Alexis, who held the rank of an Aviation Electrician's Mate 3rd Class and had served full-time in a logistics support squadron in Forth Worth, according to the Navy.
  
The shooting left Washington on edge and there was a security scare hours later at the White House when a man who apparently threw firecrackers over a fence at the US president's residence was swiftly arrested.
"There is definitely a pattern of misconduct during his service," a US military officer, who spoke on condition of anonymity, told AFP.