The trial of suspended Waltham Police Chief Thomas LaCroix is scheduled to begin Thursday in Concord District Court, according to the Middlesex district attorney’s office. LaCroix is facing allegations that he assaulted his wife and a female neighbor in separate incidents in Maynard last June. LaCroix is under house arrest and is required to wear a GPS monitoring bracelet. He has earlier declined to comment on the incidents. LaCroix, who has pleaded not guilty, was placed on paid administrative leave after his arrest, allowing him to continue to collect his $146,305 annual salary.