A man has shot and killed his suspected girlfriend before carrying out a failed suicide attempt in the US state of Colorado, authorities say.Witnesses said they heard gunfire at about 9:00 p.m. local time on Sunday, in the northern area of the city of Denver, police reported. Authorities added that the unidentified man shot to death his alleged girlfriend, before shooting himself in the chest in a suspected suicide attempt. The man was rushed to a local hospital where he lies in serious condition. The shooting happened outside a home with several family members present, though police did not provide information on a motive. The incident comes amid growing calls across the US for legislative action to control free access to guns, especially assault weapons. Every year, more than 30,000 people are shot and killed in the United States, and more than a million people have been killed with guns in the country since 1968.