The two young men accused of carrying out the massacres in Buffalo and Uvalde followed a familiar path: They legally bought semiautomatic rifles right after turning 18, posted images intended to display their strength and menace — and then turned those weapons on innocent people.

As investigators and researchers determine how the tragedies unfolded, the age of the accused has emerged as a key factor in understanding how two teenagers became driven to acquire such deadly firepower and how it led them to mass shootings.

They fit in a critical age range — roughly 15 to 25 — that law enforcement officials, researchers and policy experts consider a hazardous crossroads for young men, a period when they are in the throes of developmental changes and societal pressures that can turn them toward violence in general, and, in the rarest cases, mass shootings.