A man accused of scaring an elderly North Carolina woman to death after breaking into her home following an attempted holdup at a credit union pleaded not guilty Thursday to federal charges in the case.

Larry Whitfield, 20, of Charlotte entered the plea before federal Magistrate Judge Carl Horn III, according to federal court documents. The judge approved the man's request for a court-appointed attorney.

Whitfield was indicted last month on several federal charges related to the attempted armed robbery of a Gastonia credit union and the death of Mary Parnell, 79, the documents show.

Prosecutors argued that the woman was scared to death during a home invasion in which she died of a heart attack. But, according to a police report, Parnell told police he never touched the woman.

Whitfield faces federal charges of conspiracy to commit a violent crime, using firearms in a bank robbery to aid and abet another and causing a death as a result of a bank robbery, the documents show. If convicted on the charges, he could faces a maximum of life in prison.

Police said Whitfield and another man went to a Gastonia credit union armed with semiautomatic weapons on Sept. 26, but were locked out by the bank's security doors. They drove off and crashed their car a few miles away. Police said Whitfield then forced his way into Parnell's home.

An autopsy report said Parnell died of a heart attack brought on by "stress during home invasion." She also had an enlarged heart, was overweight and had advanced liver disease, kidney disease, hypertension, heart disease and diabetes. Those illnesses were listed as secondary factors in her death.

While no evidence points to any physical contact between Whitfield and Parnell, authorities said his attempted armed robbery charge makes him liable for her death under a felony murder rule. Her death, prosecutors said, occurred during the commission of a felony.

Whitfield was charged by the state with first-degree murder and several other charges related to Parnell's death and the attempted armed robbery. He has not yet entered a plea on the state charges.

His attorney on the state charges has told Whitfield and his family not to speak about the case, and no attorney is yet listed for the man on the federal charges.

Whitfield is being held without bond in a federal detention center in Charlotte.