Loudoun County police have charged a Herndon man with the shotgun murder of his 28-year-old roommate, whose decomposed body was discovered near a deserted barn in the Arcola area of the county Feb. 27.

John Gregory Cross, 27, an unemployed house painter, was being held without bond yesterday on charges of capital homicide and robbery. Cross, accompanied by his attorney, surrendered to authorities Monday night.

If convicted, he could face the death penalty.

Cross' arrest concluded a six-week investigation into the slaying of Gregory Gerachis, an unemployed mechanic who police said shared an apartment with Cross in Herndon. Gerachis' body was found by a man walking his dog on farmland near the Fairfax County line off state Rte. 616. w

Authorities said the body, identified by the FBI from fingerprints and tatoos, had been partially hidden under loose pieces of lumber. Gerachis had been shot in the back with a 12-guage shotgun near the spot where the body was found, police said.

An autopsy placed the time of his death around Jan. 17, more than a month before the body was discovered. Gerachis, a Lovettsville native, had been out of touch with his family there, police said, and was never reported missing.

Police said evidence that Gerachis had been robbed included a chain, fastened to the belt, that typically attaches to certain kinds of wallets and which is preferred by motorcyclists. Whatever had been attached to the chain was missing, police said.

Police said a shotgun they suspect was the murder weapon has been recovered from a third party who allegedly purchased the gun from Cross.