Suspect in French teacher's killing swears allegiance to ISIS, sparking heightened terror alert

A 20-year-old Russian immigrant fatally stabbed a teacher and wounded others at a French high school.
The attacker declared allegiance to ISIS and hatred for French values in a recorded message.
French authorities are investigating the main suspect, his teenage brother, and 15-year-old cousin.
France has raised its national terror alert level and deployed thousands of troops in response.
The attack comes amid tensions in the Middle East and memories of past terrorism in France.