A gunman has killed a hostage and himself during a stand-off at Nasa's Johnson Space Center in Houston, Texas.
 The alert comes after this week's massacre in Virginia | Police, who had surrounded the scene and entered when they heard a gunshot, also found a second hostage, a woman, who was alive but tied up with tape. Police Capt Dwayne Ready said officers were called to the scene at about 1340 (1840 GMT) after a man was seen with a gun and two shots heard. The gunman was not identified but was reported to be an employee at the site. He was described as a white male aged between 50 and 60. Two found dead Capt Ready said police were making contact with the suspect when they heard a shot. "Believing that the suspect may have shot himself the decision was made to make entry," he said. "As our Swat team members made entry they did indeed determine that the suspect shot himself one time to the head. He appears to be deceased at this time. "Also, on the same floor there was one other hostage that was shot - we believe that may have occurred in the early minutes of this whole ordeal - and another hostage that was unharmed." The survivor was female while the dead hostage was male, he said. Police could not confirm the identity of either the suspect or the hostages. School secured A Nasa contractor, Jacobs Engineering, earlier told the BBC that one of its employees was involved in the incident. After the gunman was reported, Building 44, housing communications equipment and engineering offices, was evacuated and staff across the sprawling complex were told to remain inside their buildings. The Houston police department told the BBC they sent a helicopter, a canine unit and a special weapons team to the space centre. Negotiators were also on the scene and a bomb squad was sent as a standard precaution. The Johnson Space Center contains Nasa's mission control which oversees the agency's space flights. An intermediate school near the building was also secured for several hours. The stand-off came less than a week after a gunman killed 32 students and teaching staff at Virginia Tech university before killing himself. The BBC's Adam Brookes in Washington says there has been a rash of security alerts across the US, which is also marking the eighth anniversary of the Columbine school massacre in which 15 people died. | 
