field is here with the latest on that. >> chris, this is somebody authorities were watching. there was a tip from the young man's father facebook messages and conversations being closely monitors. once he had the weapons in hand authorities felt they could make their move. veteran boston police officer compelled to alert authorities about his 23-year-old son making alarming comments to his father. the son now standing accused of terrorist plotting on behalf of isis. alexander was arrested and charged on july 4th for position of firearms allegedly purchased to carry out and attack. >> this individual began to look at isis what they were doing and begin to change themselves. >> reporter: according to court documents unsealed monday alexander has a history of mental illness and became obsessed with islam 18 months