Law enforcement authorities faced questions and criticism Thursday over how much time elapsed before they stormed a Texas elementary school classroom and put a stop to the rampage by a gunman who killed 19 children and two teachers.

Investigators were also unable to say with any certainty whether an armed school district security officer outside Robb Elementary in the town of Uvalde exchanged fire with the attacker, 18-year-old Salvador Ramos, when Ramos first arrived on Tuesday.

The motive for the massacre — the nation’s deadliest school shooting since Newtown, Connecticut, a decade ago — remained under investigation, with authorities saying Ramos had no known criminal or mental health history.

During the siege, which ended when a U.S. Border Patrol team burst in and shot the gunman to death, frustrated onlookers urged police officers to charge into the school, according to witnesses.

Moscow pressed the West on Thursday to lift sanctions against Russia over the war in Ukraine, seeking to shift the blame for a growing food crisis worsened by Kyiv’s inability to ship millions of tons of grain and other agricultural products because of the conflict.

Britain immediately accused Moscow of “trying to hold the world to ransom” and insisted there would be no sanctions relief.

Ukraine is one of the world’s largest exporters of wheat, corn and sunflower oil, but the war, including a Russian blockade of its ports, has prevented much of that production from leaving the country, endangering the world food supply. Many of those ports are also now heavily mined.

Kremlin spokesman Dmitry Peskov tried to put the blame for the crisis squarely on Western sanctions.