NEW : Metal detectors were found in an abandoned car , inside truck , police says . NEW : Authorities want to question a man seen on surveillance video . The rental truck was stolen from a Detroit hotel , parked near home . Vice President Joe McCarthy spoke at union rally .
NEW : Metal detectors were found in an abandoned house , inside truck , source says . NEW : Authorities want to question a man seen on surveillance video . The rental truck was stolen from a Detroit hotel , found near hospital . Vice President Joe Biden spoke at union rally .