A gunman has killed at least five people and injured four others, before fatally shooting himself in the head during a birthday party in the US state of Texas. The shooting spree occurred on Saturday in the party held at a roller-skating rink in the city of Grand Prairie, Texas, a foreign news agency reports. Police say the shooter, whose name has not been announced, was one of the organizers of the party. According to the officials, the wounded were sent to nearby hospitals for treatment, although their conditions was not immediately known. According to 2007 statistics, the United States has 90 guns for every 100 citizens, making it the most heavily armed society in the world.