Johnson Space Center
Last Updated: Friday, 20 April 2007, 22:42 GMT 23:42 UK
Gunman kills hostage at Nasa base
The alert comes after this week's massacre in Virginia
Police in the US city of Houston, Texas, say a gunman at the Nasa space centre has killed one hostage before killing himself.
Capt Dwayne Ready said a second hostage was found at a building at the Johnson Space Center tied up with tape.
Police were called to the scene at about 1340 (1840 GMT) after a gunman was reported and two shots heard.
Capt Ready said an additional gunshot was heard as police were making contact with the suspect, a white male.
A Nasa contractor, Jacobs Engineering, earlier told the BBC that one of its employees was involved in the incident.
The Houston police department told the BBC they had 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 building, called Building 44, houses communications equipment and engineering laboratories.
The Johnson Space Center contains Nasa's mission control which oversees the agency's space flights.
The centre's staff, numbering several thousand across the sprawling complex, were initially told to remain in their buildings but after several hours were allowed to leave the complex.
An intermediate school near the building was also secured for several hours.
The alert comes 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.
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