By Peter Allen & Benedict Tetzlaff-Deas Shocking footage shows the moment masked gunmen surround a prison van as two guards are killed anda ‘highly dangerous’ criminal escapes. The attack on the prison vehicle by four men took place this morning as the convoy was returning to Evreux jail following a court hearing in Rouen. Two prison staff were killed and three ‘seriously injured’, France’s justice minister confirmed. A ‘highly dangerous’ drugs gang boss remains on the run after getting out of the prison van into one of the assailant’s cars. Now, new video footage taken from the back of a bus …