State police are investigating a Texas couple with a hoard of high-powered weapons — including an AR-15 with a grenade launcher and bump stock — after Tewksbury police raised suspicions they were staking out the March For Our Lives last weekend.Francho Bradley, 59, and Adrianne Jennings, 40, both of Frisco, Texas, are being held without bail pending a dangerousness hearing tomorrow after they were arraigned for breaking numerous firearms laws — and are facing the nation’s first charges for possession of bump stocks.