The gunman who murdered 19 children and two teachers in Uvalde, Texas, on Tuesday crashed his truck outside Robb Elementary School at roughly 11:30 am. He "was inside the school for roughly an hour," The New York Times reports, before a tactical unit of four Border Patrol agents breached the classroom where the shooter was holed up and shot him dead around 1 pm. In that hour-long period, "frustrated onlookers urged police officers to charge into the Texas elementary school," The Associated Press reports. Juan Carranza, who witnessed the events from his house across the street, told AP he saw women shouting "Go in there! Go in there!" at the officers after the attack began, but they did not go in. Javier Cazares, whose 4th grade daughter, Jacklyn Cazares, was killed in the shooting, told AP he suggested to fellow fathers that they "just rush in because the cops aren't doing anything like they are supposed to." Police held them back, but "we wanted to storm the building," Cazares told The Washington Post. "We were saying, 'Let's go' because that is how worried we were, and we wanted to get our babies out." Authorities haven't provided a clear timeline of events, but Texas Department of Public Safety (DPS) spokesman Travis Considine said the gunman, 18-year-old Salvador Ramos, "encountered" a school police officer before entering the building and "they exchanged fire," leaving the officer wounded. Two Uvalde officers who arrived and tried to get inside were wounded in another exchange of gunfire with Ramos, he said. Ramos then entered a 4th grade classroom and "barricaded himself by locking the door and just started shooting children and teachers that were inside that classroom," DPS Lt. Christopher Olivarez told CNN. "Much of how events unfolded remains unclear," including whether police "could have intervened earlier to prevent Ramos from reaching the classroom" or entered the locked classroom sooner, the Post reports. The Border Patrol agents "had trouble breaching the classroom door and had to get a staff member to open the room with a key," AP reports, citing a law enforcement official familiar with the investigation.  "Ramos was in the room for some time before police officers entered, and it was unclear whether he killed the students when he first barricaded himself inside or just before the police breached the room,"  the Post reports. "Shots were still being heard at 12:52 pm." What is clear is law enforcement officers were among those who suffered personal losses Tuesday. One of the slain teachers, Eva Mireles, was married to a Uvalde schools police officer, and a sheriff's deputy's daughter was among the children killed in Mirales' classroom.