The U.S. Marshals Service has elevated the week-long manhunt for Paul Michael Merhige to a "major case,'' allowing the agency to devote "significantly more federal resources'' to finding the man who allegedly shot six family members at a Thanksgiving Day gathering -- killing four of them.

The marshals service has increased its reward for information on Merhige to $25,000, authorities said at a news conference Thursday in Palm Beach County.

Merhige, 35, indicated he had a history of mental problems and a ``strong resentment toward several family members,'' according to the marshals website.

Merhige, the marshals said, planned his escape and took pains to avoid law enforcement detection.

"He has a plan. He's following his and we're following ours,'' said deputy marshal Manny Puri. "We need to catch him before anything else happens.''

The marshals said in a statement they suspect Merhige is using only cash. He has made contact with no known associates by phone or e-mail.

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