A gun suspect on house arrest swapped his prosthetic leg and its attached GPS ankle monitor for a spare limb and went on the loose, shooting a man to death while authorities believed he remained inside his home, police in Washington, D.C., said.

Quincy Green, 34, appeared at first to have a strong alibi for the killing last month: A GPS monitor attached to his body that showed he hadn't moved in days. But the tracker had been mistakenly attached to a prosthetic leg, allowing Green to trade limbs and leave the house, according to The Washington Post, which cited court documents.

Green was ordered confined to his home in April while awaiting trial on gun possession charges. For reasons that authorities are still investigating, a privately contracted technician placed the GPS monitor on Greens prosthetic limb.

Green left the house May 19, authorities said. During the outing, he shot 44-year-old Dana Hamilton to death, according to police, who didn't disclose the motive.