Cindy Romero was in the living room of the small apartment she shared with her husband in Aurora, Colo., when she heard a commotion in the hallway. It was before midnight on a Sunday last August. Romero, 60, was sitting on the floor watching a feed on her phone from a security camera she had recently placed outside her door. Six young men carrying pistols and what appeared to be an assault rifle with a scope were milling around on the landing, focused on the door of an apartment across the hall where a friend of hers, a migrant from Venezuela, had been living.

The presence of young men with guns in the apartment complex, called the Edge at Lowry, was not a rarity. Mostly recent migrants from Venezuela, they had grown more brazen in recent months; she’d seen them selling drugs out of the parking lot and snorting a drug cocktail known as tusi or pink cocaine, at kitchen tables in ground-floor apartments that didn’t have curtains. Their loud parties outside her window would last all night. In the stairwell, she passed groups of men with guns tucked into their waistbands. She had called the police dozens of times, though officers seldom responded; they didn’t seem to take the problem seriously.

Romero took in the fish-eye view and was frightened: This time the men, dressed in shorts and athletic pants, T-shirts and baseball caps, faces mostly uncovered, looked as if they were on a mission. They opened the door of the neighboring apartment and walked in but didn’t seem to find what they were looking for. Then they disappeared back down the stairs.

Less than 10 minutes later, Romero and her husband heard shouting outside. “Shut your mouth!” someone yelled in Spanish. (Romero, an American citizen whose father was of Mexican descent, knew enough Spanish to make out the words.) Then came the sounds of a gunfight. “There were five to six different calibers of weapon,” Romero said in one of several interviews she gave afterward to local and national news outlets. She and her husband would later find bullet holes in both of their cars; the windows of other tenants’ cars were shattered.

This time the police responded, following a trail of blood to a nearby alley, where officers found the victim of the shooting — Oswaldo José Dabion Araujo, the Venezuelan man who had lived across the hall from Romero. They managed to get him to a hospital, where he would eventually die of his wounds.