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DALLAS (AP) _ Investigators are trying to determine if there is a link between a pipe bomb blast that injured the son of a Washington, D.C., businessman and the disappearance of the victim's stepbrother, a newspaper reported Sunday.

The missing stepbrother, Prescott W. ``Scott'' Sigmund, 34, had been having financial problems and argued with his father over a large credit card bill, The Dallas Morning News reported.

Authorities have not declared Sigmund a suspect in the July 12 blast that critically injured Wright Sigmund, 21, and have theorized the bomb was meant for the victim's father, insurance broker Donald Sigmund.

The bomb detonated in the underground parking garage at Sigmund's company, Wolf & Cohen Financial Services. Wright Sigmund remained in critical condition Sunday at a Washington, D.C., hospital.

Also Sunday, police reported that Scott Sigmund's black BMW was found at the Vienna, Va., Metro Station. Federal Alcohol, Tobacco and Firearms agents were planning to examine it.

Three days after the blast, he had told his wife he was going to a seminar in nearby Rockville, Md., and hasn't been seen since, police said.

Family members in Dallas said he disappeared one day before he was to have taken a police polygraph. But they contend the stepbrothers had a good relationship.

``Scotty flew down to Dallas when Wright graduated from high school,'' said Claire Phillips, Wright's mother.

Wright Sigmund followed in the footsteps of his stepbrother and his father, attending Washington & Lee University in Virginia. Family members and friends said Wright Sigmund had talked about the possibility of taking over the family business when his father retires.

The older sibling quit the firm in 1997.

Federal agents and local police removed a computer and boxes of documents from Scott Sigmund's Maryland home Wednesday, looking for letters or e-mails that might yield clues to his whereabouts.