MOSCOW (AP) — Russian officials say an unidentified assailant has detonated an explosive device next to a patrol vehicle in Moscow, killing himself and a police officer and leaving two other officers injured. The attack Tuesday happened minutes after midnight near the Savyolovsky Train Station in the Russian capital’s downtown, according to Moscow’s branch of the Interior Ministry. Russia’s Investigative Committee said it has launched a probe into the attack. It didn’t name the assailant or give any information about his possible motives or any further details. Tuesday marks the fourth anniversary of Russian President Vladimir Putin’s decision to send troops into Ukraine.