COLORADO SPRINGS, Colo. -- A man serving a life sentence in Colorado for murdering a teenage girl has claimed responsibility for as many as 48 slayings across the country dating back more than three decades, authorities said Thursday. Robert Charles Browne, 53, told authorities the slayings occurred from 1970 until his arrest in 1995. He was in court Thursday to plead guilty to one of those killings - the death of another girl in Colorado in 1987. Authorities so far have been able to corroborate his detailed claims in seven slayings - three in Louisiana, two in Texas, one in Arkansas and the two in Colorado, El Paso County Sheriff Terry Maketa said. He said Browne's claim of 48 murders could be credible. "It's possible he's exaggerating, but I don't think you can conduct business assuming he's exaggerating," Maketa said.