MONTOURSVILLE (AP) — Pennsylvania State Police say blood has been discovered on the car of the missing adult daughter of a couple who were robbed at gunpoint and bound with duct tape before their home was set ablaze.

Michelle Inch hasn't been seen since Tuesday, a day before her parents were robbed by two masked men at their home near Montoursville. The 33-year-old's boyfriend and another man are in custody in the attack. Inch's black Honda Accord was found Thursday near Canton in Bradford County, about 50 miles north of her parents' home.

A preliminary forensic examination of her car turned up blood on the outside of the vehicle, according to police who say they now suspect foul play in the case. Police added in a statement released Saturday that they are continuing to search places that Inch and her boyfriend Michael Houseweart, 27, of Canton, were known to frequent.

Police said Inch and Houseweart had been living with her parents but had a falling out with them recently. Houseweart and Brian Vroman, also 27 and from Canton, are accused of breaking into the home early Wednesday and are being held without bail on charges including robbery, arson and attempted homicide.

Authorities said two ski masks like the ones used in the robbery were found in Vroman's car, and surveillance video showed the two men arriving in Michelle Inch's car at a Montoursville-area Wal-Mart and buying duct tape and gloves less than two hours before the attack.

Linda Inch, 66, managed to free herself and ran to the neighbors for help, police said. Firefighters had to break down the front door to rescue 71-year-old Gary Inch, who was found unresponsive on an upper floor. Both victims were taken to a hospital for treatment of smoke inhalation. Police said a flat-screen TV, a poker set, cash and two cellphones were stolen.