18, 2013 file photo, employees of the Washington Navy Yard line up to enter through a gate two days after a gunman killed twelve people and was killed himself inside. A new report says contract guards who protect federal facilities are receiving uneven training on responding to shootings like the one last month at the Washington Navy Yard. The report was released Wednesday by the Government Accountability Office. A summary of the report was presented at a House subcommittee hearing on securing federal facilities. The report says officials at five guard companies said their guards had not received training on what to do when a gunman is opening fire. WASHINGTON (AP) - Federal officials who oversee the security clearance process for government employees were to face a Senate committee investigating the events leading up to a deadly shooting at the Washington Navy Yard. The hearing Thursday before the Senate Committee on Homeland Security and Governmental Affairs is to examine the adequacy of background checks and the security clearance system for federal employees and contract workers. It comes as officials investigate how Aaron Alexis, a 34-year-old defense contractor, was able to acquire and maintain a secret clearance despite a series of violent outbursts, repeated brushes with the law and concerns about his mental health. The former Navy reservist killed 12 people inside the Navy Yard building where he worked Sept. 16 before being fatally shot by police. He entered the property with a valid security badge. "The tragic events at the Navy Yard highlight the need to be ever-vigilant in ensuring that individuals entrusted with access to classified information, and, more generally, other individuals with logical and physical access to federal facilities and information do not present either a national security risk or a personal security risk," Elaine Kaplan said in remarks prepared for the Senate hearing. Kaplan is acting director of the Office of Personnel Management, which oversees more than 90 percent of background investigations for the federal government. President Barack Obama has also ordered the White House budget office to examine security standards for government contractors and employees across federal agencies. Concerns about weaknesses in the security clearance system have surfaced not only with Alexis but also with National Security Agency leaker Edward Snowden and Army Pvt. Chelsea Manning, currently imprisoned for leaking classified documents. Many national security experts have long argued that the security clearance process is antiquated and in need of modernization. Given recent events, I think we have to ask whether the system is fundamentally flawed," Sen. Tom Carper, the committee chairman, said in prepared remarks. Defense officials have said that when Alexis applied for security clearance with the Navy, he lied about a 2004 arrest in Seattle for shooting the tires of an unoccupied vehicle and he failed to disclose thousands of dollars in debts. An FBI fingerprint check revealed the arrest, but an investigative report from an OPM contractor omitted the fact that Alexis had fired shots, the Seattle police department did not turn over records of the arrest and no charges were filed. He was granted a secret clearance in 2008 and held onto it despite multiple subsequent encounters with police, including a 2010 arrest in Texas, where a neighbor told police she was nearly struck by a bullet fired from his downstairs apartment. Kaplan said her staff has advised her that Alexis's file "complied with all applicable standards," but that OPM's office of internal oversight and compliance is reviewing the matter. One month before the Navy Yard shooting, Alexis called police in Rhode Island to the hotel where he was staying and complained about voices wanting to harm him, according to the police report. The FBI has said he believed he was being bombarded with extremely low frequency radio waves. Four senators on Wednesday introduced legislation to require more frequent checks on government employees and contractors who are awarded security clearances. Clearances last for five or 10 years depending on the level of secrecy required in the job and the level of clearance. The bill requires OPM to do at least two audits of every security clearance at random times over each five years the clearance is in effect. Surprise audits would send the message that "you never know when the government is going to find out," so it's better to come forward with the information voluntarily, said one sponsor, Democratic Sen. Claire McCaskill of Missouri. Associated Press writer Pauline Jelinek contributed to this report.