LONDON (AP) — Encrypted messaging services like WhatsApp must make their platforms accessible to intelligence agencies, a top British security official declared Sunday amid reports that the Westminster attacker used the service minutes before his assault on Parliament. British police investigating the attack on Parliament that claimed four victims and wounded dozens say they still believe the assailant acted alone and they have no information indicating that further attacks are planned. Deputy Assistant Commissioner Neil Basu said it may never be possible to fully determine the motives of attacker Khalid Masood, who was shot dead Wednesday after running over pedestrians with an SUV on London's Westminster Bridge and fatally stabbing a policeman guarding Parliament.