No one hears them scream. In Denver, Colorado, dozens of police and tracker dogs were back scouring rail yards and abandoned lots early yesterday morning after the discovery in an overgrown field near Union Station of two more bodies - this time headless - of homeless men. The discovery takes to at least seven the number of homeless people killed in Denver since September and is set to highlight the widening tragedy of homelessness in an economy high on its longest peacetime boom. The two bodies are the first found since the arrests late last month of three young men in connection with the fatal beating of one of the first dead vagrants, 49-year-old Melvin Washington. Violence against the homeless is seldom reported, much less investigated in depth, even when it is fatal. There is usually no one to report them missing and few credible witnesses after the fact. In Denver, that is starting to change as dozens of officers now find themselves assigned to the case fast drawing national attention. Yesterday's bizarre discovery has prompted new intrigue but so far yielded few leads. Previous victims had been beaten to death. These two men were decapitated but it is not known how. Early investigations suggest one victim was killed more than a month ago. A few hundred metres away was another body of a man killed a week ago. In classic fashion, it could be days before the bodies are identified. 'My only hope is that some good comes out of all this violence,' said Barbara Duffield, a researcher with the National Coalition for the Homeless in Washington DC. 'Maybe, just maybe, it will start to wake us up from our complacency. Young people think the homeless people on the streets across urban America have always been there. 'Well, they haven't. This has all happened within a generation. It is a national disgrace. 'For the ones people see on the streets, there are thousands of invisible homeless out there, struggling by and keeping out of trouble.' Activists such as Ms Duffield point to an array of government figures that suggest homelessness - seen as a 1980s problem - is actually getting worse despite an economy that is bringing unprecedented wealth to the middle classes. While many ordinary Americans believe that most homeless people are drifters or misfits there by choice or through crime, mental illness or addiction, surveys suggest otherwise. Low-end rents - rising in part through inner-city property booms and 'gentrification' - are soaring quicker than the comparatively stagnant minimum wage and making it tricky for increasing numbers of families. For many, there is simply a lack of affordable housing. Federal officials admit the problems but say at the moment there is no 'grand plan' to turn things around despite an array of election slogans. A two-year study by the Department of Housing and Urban Development found that the number of units with rent below US$300 (HK$2,230) a month dropped by 13 per cent - about 950,000 apartments - over the past two years. This figure is expected to contribute to what some activists believe will be a damning portrayal in a survey across 30 cities now being prepared for the annual Conference of Mayors. Last year the conference heard that requests for emergency shelter rose on average by 11 per cent across American cities, with appeals from families rising 15 per cent. The survey also found that families now comprised 38 per cent of the homeless population, with single men still the single biggest category with 45 per cent. About 24 per cent were considered mentally ill and 38 per cent substance abusers. Twenty-two per cent were military veterans. 'The city officials report that the strong economy has had very little positive impact on hunger and homelessness. In many cities, conditions are likely to decline further next year,' the report, due to be updated next month, noted. Denver is considered one of the most desperate cities, with figures rising far above the national average with an estimated 5,800 homeless on the streets compared with 3,000 a decade ago, fuelled in large measure by rising rents. Shelters are now virtually full each night as the drifters worry about being out on the streets. Most now roam in groups for protection. 'Until recently, we used to think they were all here because Denver is a great place to be homeless,' a local shop-keeper said. 'It is in the middle of America so you can bum here from just about anywhere for a good climate and there is plenty of charity doling out free food and shelter. No one is saying that now. 'These deaths have made us think. Not everybody is out there because they want to be. The constant threat of violence and death is the last thing they need.'