MONROVIA, Liberia — Liberian security forces fired with “complete disregard for human life” into crowds of civilians protesting a blanket Ebola quarantine over the summer, killing one teenager and seriously wounding another young man, according to the first independent investigation of the deadly clashes.

The findings directly contradict repeated assertions by the security forces, including the American-trained Liberian Army, that soldiers fired shots only into the air to enforce the quarantine of residents, which had been imposed against the advice of international Ebola experts and the government’s own health officials.

A 15-year-old boy bled to death after suffering bullet wounds to both legs during the protest. The investigation — conducted by the Liberian Independent National Commission on Human Rights, but not yet made public — concluded that unless “it was a magic bullet,” a round “shot in the air cannot fall from above and shatter somebody’s legs.” A copy of the report was obtained by The New York Times.

Liberian and foreign critics say that the mishandling of the quarantine is one of several missteps that have deepened public distrust of the government, a rift that has helped fuel the spread of Ebola since the outbreak began months ago.