text1: Three police officers have been killed by a gunman in Pittsburgh - the second mass shooting in the US in 24 hours. The officers were responding to an emergency call from the house of the gunman, named as Richard Poplawski, 23. Police said he was waiting, armed with rifles and a bulletproof vest. He shot two officers as they entered the house, and a third who tried to help them. He then traded gunfire with police for four hours before being injured and giving himself up. His friends said he had recently lost his job, and was worried that US President Barack Obama was about to ban guns.
text2: In Pittsburgh the police killed a gunman.